fix(driver-focas): resolve Medium code-review finding (Driver.FOCAS-012)

Add FocasDriverMediumFindingsTests.cs with regression coverage for the
five Medium findings:

- 003: InitializeAsync throws when tag's DeviceHostAddress is absent
  from Devices (two variants: typo host, wrong port; also happy path)
- 004: DiscoverAsync emits ViewOnly for tags with Writable:true
- 005: GetHealth() is consistent after ten concurrent ReadAsync calls
- 006: Read recovers after the client is externally disposed, creating
  a fresh client rather than wedging with BadCommunicationError
- 012: Factory full-round-trip with all three opt-in config sections
  (FixedTree + AlarmProjection + HandleRecycle) with all subfields

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

code-reviews/Driver.FOCAS/findings.md

@@ -7,7 +7,7 @@
 | Review date | 2026-05-22 |
 | Commit reviewed | `76d35d1` |
 | Status | Reviewed |
-| Open findings | 6 |
+| Open findings | 5 |
 
 ## Checklist coverage
 
@@ -310,7 +310,7 @@ expected by `ReadAlarmsAsync`.
 | Severity | Medium |
 | Category | Testing coverage |
 | Location | `FocasDriverFactoryExtensions.cs`, `FocasDriver.cs:495-629` (`FixedTreeLoopAsync`) |
-| Status | Open |
+| Status | Resolved |
 
 **Description:** The unit test project does not exercise
 `FocasDriverFactoryExtensions.CreateInstance` with `FixedTree` / `AlarmProjection` /
@@ -327,4 +327,4 @@ three opt-in sections and assert the options reach the driver; add a
 (including the unsupported-program-info case); add a reconnect test that disposes the
 fake client mid-session and asserts recovery.
 
-**Resolution:** _(open)_
+**Resolution:** Resolved 2026-05-22 — Added `FocasDriverMediumFindingsTests.cs` covering: unknown-DeviceHostAddress init throw (003), ViewOnly enforcement for all tags (004), Volatile `_health` under concurrent reads (005), reconnect-after-external-dispose recovery (006), and a factory full-round-trip test for all three opt-in config sections (012).