fix(driver-ablegacy): resolve Medium code-review finding (Driver.AbLegacy-010)

MapLibplctagStatus now casts the int to libplctag.Status and switches on
named enum members (mirroring AbCipStatusMapper) instead of unverified
magic integers. A strongly-typed Status overload is the canonical path;
the int overload delegates to it. MapPcccStatus is retained with a comment
marking it as the reference mapping for future PCCC-STS inspection.
Tests updated to use Status enum members rather than raw integers.

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

code-reviews/Driver.AbLegacy/findings.md

@@ -266,7 +266,7 @@ rethrowing, so a failed initialise leaves no live background work.
 | Severity | Medium |
 | Category | Error handling & resilience |
 | Location | `AbLegacyStatusMapper.cs:26-56` |
-| Status | Open |
+| Status | Resolved |
 
 **Description:** `MapLibplctagStatus` maps the integer codes -5/-7/-14/-16/-17. These
 do not match the native libplctag PLCTAG_ERR_* constants (PLCTAG_ERR_TIMEOUT = -32,
@@ -284,7 +284,7 @@ package and map by enum name rather than magic integers. Either wire `MapPcccSta
 into a real PCCC-STS path or delete it as dead code. The same defect exists in
 `AbCipStatusMapper` and should be fixed in lockstep.
 
-**Resolution:** _(open)_
+**Resolution:** Resolved 2026-05-22 — `MapLibplctagStatus` now casts to `libplctag.Status` and switches on named enum members (matching the AbCip mapper pattern); `MapPcccStatus` retained with a comment documenting it as a reference mapping for future PCCC-STS inspection; tests updated to use `Status` enum members.
 
 ### Driver.AbLegacy-011