fix(sql): browse-commit states a topByTimestamp row selector (#552)

`RawBrowseCommitMapper.BuildSqlTagConfig` emitted a WideRow blob carrying only
table + columnName. A wide-row tag must also say WHICH row it reads, so both
`SqlEquipmentTagParser` (the runtime authority) and `SqlTagConfigModel.Validate`
(the authoring gate) refused it — a browse-committed Sql tag was never readable,
first silently as BadNodeIdUnknown and, since #551 put the gate on the import,
loudly at commit.

`SqlBrowseSession` now states a fourth address field: the table's preferred
date/time-typed column, computed from the columns its attributes call ALREADY
read (no extra catalog round-trip). Candidacy is decided by
`ISqlDialect.MapColumnType` reporting `DriverDataType.DateTime` — never by column
name, which would order a wide-row read by a string column that merely looks like
a timestamp. Multiple candidates tie-break on FIRST IN CATALOG ORDER (every
dialect's column SQL orders by ordinal position), so the pick is stable across
calls and servers; it is a visible, editable default the typed editor round-trips.

No candidate (a table with no date/time column) is an operator-actionable refusal,
not an invented selector: the only remaining selector is a whereColumn/whereValue
pair whose value is data, not schema, so `DescribeUncommittableLeaf` refuses that
leaf by name, names the table, and points at the tag editor.

The session and the mapper now agree via `SqlBrowseAddressFields` constants rather
than two independently spelled string literals — a disagreement there is silent,
and is exactly the shape this defect had.

`RawTagConfigGateTests`' Sql leg flips from "records the gap" to "browse-commit
output passes the gate", with the no-candidate case pinned as its own test.

docs/drivers/Sql.md

@@ -169,6 +169,33 @@ Browse works against all three constructed providers; the catalog query is the d
 (`INFORMATION_SCHEMA` on SQL Server and Postgres — with `pg_catalog` / `information_schema`
 themselves excluded — and the `ALL_*` views on Oracle).
 
+### The committed row selector (Gitea #552)
+
+A browse-committed column becomes a **WideRow** tag, and a wide-row tag must say *which row* it reads
+— the table and column alone are not a binding. The browse session therefore states a fourth address
+field alongside schema/table/column: the table's preferred **date/time-typed** column, which the
+commit writes as `rowSelector.topByTimestamp` ("read the newest row"). Before this the commit emitted
+a selector-less blob that `SqlEquipmentTagParser` and the authoring gate both refuse, so no
+browse-committed Sql tag was ever readable.
+
+Two properties of the choice are deliberate:
+
+- **Candidacy is by declared TYPE, never by column name.** The session asks
+  `ISqlDialect.MapColumnType` for `DriverDataType.DateTime` — the same metadata the browse tree already
+  renders per column. A name heuristic (`*_ts`, `*time*`) would happily order a wide-row read by a
+  *string* column called `timestamp`, binding the tag to whichever row sorts last lexically.
+- **The tie-break is first in catalog order** (every dialect's column query orders by ordinal
+  position), so the pick is stable across calls, connections and servers. On a
+  `CreatedUtc`/`ModifiedUtc` pair it takes the earlier-declared one. It is a **visible, editable
+  default**: the typed editor shows the selector and the operator can change it — to the other
+  timestamp, or to a `whereColumn`/`whereValue` pair entirely.
+
+**A table with no date/time column cannot be bound by browse, and the commit says so.** The remaining
+selector is a `whereColumn`/`whereValue` pair whose value is *data*, not schema, so nothing in a
+catalog can supply it. `RawBrowseCommitMapper.DescribeUncommittableLeaf` refuses that leaf by name,
+names the table, and points at the tag editor; no selector is invented, and the mapper's blob stays
+selector-less rather than dropping to a generic `{"address": …}` the typed editor cannot read.
+
 ## Authoring in the AdminUI
 
 - **Driver config** — `/raw` → driver node → *Configure*. Sql is a **single-connection** driver: the