docs(drivers): write the two missing driver guides (Sql, Calculation)

Closes the §7.2 priority-3 item. Sql was a shipped, merged driver with NO
user-facing documentation at all -- only design and plan files, which describe
what was intended rather than what an operator needs to author one.

Sql.md covers: SQL Server as the only constructed provider (the other four
SqlProvider names are reserved, and authoring one fails rather than falling
back), the KeyValue / WideRow tag models with worked TagConfig, Query being
rejected end-to-end, the config table with real defaults read from
SqlDriverOptions, connectionStringRef never carrying credentials into an
artifact, per-source query grouping and its case-sensitive group keys, and the
value-bound-vs-identifier-validated split that makes it injection-safe.

Calculation.md covers: what a pseudo-driver is and why it occupies a driver slot,
a Calculation-vs-VirtualTags decision table (the two are easy to confuse), the
literal-only ctx.GetTag dependency extraction and the runtime-built-path trap,
the two deploy gates, the all-deps-arrived publish gate, and the Good->Bad-once
error semantics.

Two stale claims found by checking against source rather than inheriting them:

  - The driver README's Calculation row still carried G-1 ("no typed config form,
    RunTimeout unauthorable"), fixed on 2026-07-27 by CalculationDriverForm.
  - docs/Raw.md's "one auto-created default Engine device" NEVER SHIPPED. I had
    copied it into the new doc before checking; "Engine" has zero occurrences in
    src/ and nothing special-cases Calculation at device creation. Corrected in
    both files. The config key was also wrong in my first draft: runTimeoutMs, an
    int in milliseconds, not a TimeSpan string -- and it is ignored on reinit
    because the evaluator's timeout is constructor-fixed.

Full solution: 49 suites pass; the 2 failures are the known pre-existing
environment ones (AbLegacy.IntegrationTests docker fixture, Host.IntegrationTests).
OpcUaClient.IntegrationTests, which was silently failing, is now green.

Claude-Session: https://claude.ai/code/session_015p7wGqy3YpZNCpDzTpGMKo

docs/Raw.md

@@ -70,7 +70,9 @@ Signal-level calculated tags are ordinary raw tags bound to a `Calculation` driv
 `ctx.GetTag("<RawPath>")`. See `docs/plans/2026-07-15-calculation-driver-mini-design.md` for
 the full design. Highlights:
 
-- One auto-created default `Engine` device; per-tag `TagConfig` is
+- ⚠️ **Correction (2026-07-28): the "auto-created default `Engine` device" below never shipped.**
+  `"Engine"` has zero occurrences in `src/`, and nothing special-cases `Calculation` at device
+  creation — author the device like any other. Per-tag `TagConfig` is
   `{ "scriptId": "…", "changeTriggered": true, "timerIntervalMs": 5000 }`.
 - The host feeds dependency values via the new `IDependencyConsumer` capability + a
   `DependencyConsumerMuxAdapter` on the per-node dependency mux; calc-of-calc chains work