feat(sql): implement the design §8.1 catalog identifier-validation gate (#496)

Until now ISqlDialect.QuoteIdentifier was the SOLE defence for authored
table/column names: an identifier went from the TagConfig blob straight into a
command text, bracket-quoted. The residual risk was bounded — a hostile name is
quoted into one nonexistent object, the query fails after the connection opens,
and the tag Bad-codes — but "bounded" is not "filtered", and the design promised
a filter. Both ISqlDialect and SqlServerDialect carried a doc paragraph saying so.

SqlCatalogGate + SqlCatalogLoader now resolve every authored identifier against
the live catalog at Initialize, and REPLACE it with the catalog's own spelling.
The identifier text in an emitted poll query is therefore a string this driver
read back out of ListSchemas/ListTables/ListColumns — not operator input. Quoting
becomes the backstop it was documented to be.

Decisions worth knowing before touching this:

- Substitution, not just validation. Matching is exact-ordinal first, then a
  UNIQUE case-insensitive hit: SQL Server's default collation is CI so case
  variants have always worked, and rejecting them would break valid deployments.
  An ambiguous CI match under a case-sensitive collation is refused rather than
  guessed — picking one would publish another column's data under the operator's
  node, which is worse than rejecting the tag.

- Charset check BEFORE catalog lookup. Each identifier goes through
  QuoteIdentifier for its rejection rules first, so a name carrying a control or
  Unicode format character is rejected WITHOUT its value being echoed into a log
  line (Trojan-Source). A name that passes is safe to render, which is why
  catalog-miss messages do name it — an operator hunting a typo has to see what
  they wrote. Both halves are pinned by tests.

- A rejected tag keeps its node. It is dropped from the POLLED table but stays in
  the AUTHORED table, so it still materializes and reads BadNodeIdUnknown —
  §8.1's specified outcome. My first wiring dropped it from both, which deleted
  the node instead; an existing test (ReinitializeAsync_recoversFromFaulted)
  caught it. A status code can only be published by a node that exists, and a
  missing address-space entry is far harder to diagnose than a Bad quality.

- An unreadable catalog FAULTS Initialize; it does not reject every tag. That is
  the absence of evidence about the tags, not evidence against them — rejecting
  all of them would serve a confidently-empty address space and send the operator
  hunting typos that do not exist. Zero visible schemas is treated the same way,
  because that is exactly what a missing GRANT looks like. Faulting lands
  DriverInstanceActor in Reconnecting with its retry timer running.

- Bounded load: one schema list, one default-schema scalar, then one ListTables
  per distinct authored schema and one ListColumns per distinct authored relation
  — never a full catalog enumeration, and nothing after Initialize. Every
  authored name reaches the catalog queries as a bound @schema/@table parameter,
  so building the allow-list cannot itself be an injection vector.

- ISqlDialect gains DefaultSchemaSql ("SELECT SCHEMA_NAME()"). An unqualified
  `TagValues` must resolve in whatever schema the SERVER reports; hardcoding dbo
  would be a silent lie on any estate that maps service accounts to their own
  default schema. It is a query, not a constant, because the answer is
  per-connection.

- Accepted v1 limitation: a 3-part db.schema.table (or linked-server name)
  addresses a catalog this connection cannot enumerate, so it cannot be
  allow-listed and is rejected with a message pointing at the fix — expose the
  data through a view in the connected database.

VerifyLivenessAsync's wall-clock pattern is extracted to RunBoundedAsync and
reused, so the new I/O gets the same R2-01 / STAB-14 protection rather than a
second hand-rolled copy. (It also fixes a latent bug in the extracted code: the
OperationCanceledException arm detached the wrong task.)

Tests: 24 pure gate tests + 9 end-to-end driver tests against the real SQLite
catalog + 3 new live tests against the real SQL Server on 10.100.0.35 (21 in that
suite now pass, exercising the real SELECT SCHEMA_NAME() + INFORMATION_SCHEMA
path). Verified falsifiable: bypassing the gate turns exactly the three rejection
assertions red and leaves the rest green.

SqlInjectionRegressionTests is deliberately NOT rewritten to expect
BadNodeIdUnknown. It drives SqlPollReader directly, below the gate, and pins the
quoting backstop on its own — defence in depth is only worth the name if each
layer holds independently. Rewriting those assertions would delete the backstop's
only coverage and leave the gate a single point of failure. Its scope note, which
said the gate does not exist, is updated to say why it stays where it is.

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Sql/ISqlDialect.cs

@@ -14,11 +14,13 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Sql;
 ///     parameterized in SQL, so the few that must appear as text are emitted through
 ///     <see cref="QuoteIdentifier"/>. Any code path that builds SQL by concatenating an authored tag field
 ///     <em>without</em> going through <see cref="QuoteIdentifier"/> is a defect (design §8.1).</para>
-///     <para><b>Not yet implemented:</b> design §8.1 also specifies that an authored table/column is
-///     validated against the live catalog before it is ever quoted into text, so that an unknown identifier
-///     rejects the tag. No such gate exists yet — an identifier reaches <see cref="QuoteIdentifier"/>
-///     straight from the authored <c>TagConfig</c> blob, so <b>quoting is currently the only defence</b>,
-///     not a backstop behind an upstream filter. Scrutinise it accordingly.</para>
+///     <para><b>Quoting is the backstop, not the only defence.</b> Design §8.1's catalog gate is
+///     implemented: <see cref="SqlCatalogGate"/> resolves every authored table/column against the live
+///     catalog at Initialize and <b>replaces it with the catalog's own spelling</b>, so an identifier
+///     reaching <see cref="QuoteIdentifier"/> on the poll path is a string this driver read back out of
+///     <see cref="ListSchemasSql"/> / <see cref="ListTablesSql"/> / <see cref="ListColumnsSql"/> — not
+///     operator input. An identifier that resolves to nothing rejects its tag (which then publishes
+///     <c>BadNodeIdUnknown</c>) rather than being quoted into a query against a nonexistent object.</para>
 ///     <para>Public because <c>Driver.Sql.Browser</c> consumes it — the catalog SQL <em>is</em> the browse
 ///     engine, so it is shared rather than duplicated. Implementations own their provider package;
 ///     <b>no provider-specific type appears in this signature</b> (<see cref="Factory"/> is the abstract
@@ -89,6 +91,20 @@ public interface ISqlDialect
     /// <summary>Catalog query listing schemas — the browser's <c>RootAsync</c> level. Takes no parameters.</summary>
     string ListSchemasSql { get; }
 
+    /// <summary>
+    ///     Scalar query returning the schema an <b>unqualified</b> object name resolves to for the connecting
+    ///     principal — T-SQL's <c>SELECT SCHEMA_NAME()</c>. Takes no parameters.
+    /// </summary>
+    /// <remarks>
+    ///     <para>Needed by <see cref="SqlCatalogGate"/>: a tag authored as <c>TagValues</c> rather than
+    ///     <c>dbo.TagValues</c> has to be looked up in <em>some</em> schema, and guessing <c>dbo</c> would be a
+    ///     silent lie on any estate that maps its service accounts to their own default schema. Asking the
+    ///     server is the only answer that matches how the poll query itself will resolve the name.</para>
+    ///     <para>It is a <em>query</em> rather than a name because the answer is per-connection, not per-dialect
+    ///     — the same dialect resolves differently for two different logins.</para>
+    /// </remarks>
+    string DefaultSchemaSql { get; }
+
     /// <summary>Catalog query listing tables + views in one schema — the browser's schema-expand level. Bind <c>@schema</c>.</summary>
     string ListTablesSql { get; }