LEGLINK-639: Terminology reads value-set membership status

[MikeAtPinnacle]

🛠️ Description of Changes

Extends the optional Status (active/inactive) column support from CodeSystem CSV files to ValueSet CSV files, so value-set membership status is honored independently of code-system status.

Per Irene Zhuo, value-set membership carries its own active/inactive status: an intensional value set is expanded from a code system, and a code can remain active in the code system yet be dropped from the value set's membership. When a member carries a membership status it is authoritative and overrides the code system; a member with no membership status falls back to the existing code-system rejoin (LEGLINK-580 behavior).

• Added ValueSetCode : Code carrying its own CodeStatus.
• CsvValueSetRecord gains an optional [Index(3)] Status column ([Default(Active)] + [EnumIgnoreCase]), mirroring CsvCodeSystemRecord.
• CodeGroupCacheService.ProcessValueSetCsv now accepts 3 or 4 columns (system,code,display[,status]) and selects the member type by header width — 4-col → ValueSetCode, 3-col → plain Code. This also fixes a latent bug where a 4-column value-set file threw in ProcessValueSetCsv and was silently swallowed by LoadCache, leaving that value set absent from the cache.
• CodeGroupCacheService.LoadCache now tolerates a missing trailing field for ValueSet (not just CodeSystem).
• FhirService.ResolveIsActive treats a ValueSetCode status as authoritative, falling through to the code-system rejoin only for plain Code members.

This is a Terminology-service-only change. The terminology service already emits the same Code is inactive. OperationOutcome whenever a code is inactive, so value-set-membership inactivation surfaces and categorizes through the identical Validation path — no Java, categories.json, app-config.yaml, or migration changes.

🧪 Testing Performed

• Ran the Terminology unit suite: dotnet test DotNet/ServiceTests/ServiceTests.csproj --filter "FullyQualifiedName~Terminology" → 62/62 passing (includes the new value-set tests below and the existing CodeSystem/rejoin coverage).
• Verified the branch builds clean and rebased onto the latest dev (including LEGLINK-814 duplicate-CSV-code handling) with tests still green.

🧑‍🔬 Unit Testing

• Coverage: 100.0%

• CodeGroupCacheServiceTests.LoadCache_ValueSetWithStatusColumn_LoadsValueSetCodeWithStatus — 4-col file loads ValueSetCode with the file's Active/Inactive status.

• CodeGroupCacheServiceTests.LoadCache_ValueSetBlankStatus_DefaultsToActive — blank status defaults to Active.

• CodeGroupCacheServiceTests.LoadCache_ValueSetNoStatusColumn_LoadsPlainCode — 3-col file loads plain Code (no membership status → rejoin path preserved).

• CodeGroupCacheServiceTests.LoadCache_ValueSetMixedCaseStatus_ParsesCaseInsensitively — mixed-case status parses correctly.

• FhirServiceTests.ValidateCodeInValueSet_ValueSetCodeInactive_OverridesActiveCodeSystem_ReturnsInactiveIssue — inactive membership overrides an active code system.

• FhirServiceTests.ValidateCodeInValueSet_ValueSetCodeActive_OverridesInactiveCodeSystem_ReturnsNoIssue — active membership overrides an inactive code system.

• Updated ProcessValueSetCsv_InvalidColumnCount_ThrowsException (4 columns is now valid; asserts on a 5-column header) and switched ProcessValueSetCsv_WithValidData_CallsSetCodeGroup to the shared CreateCsvReader helper.

📓 Documentation Updated

No documentation changes required — this is a data-format extension to an existing feature with no new config keys or public API surface.

Summary by CodeRabbit

• New Features

  • ValueSet CSV files now support an optional membership status column.
  • Membership statuses are parsed case-insensitively, default to Active when blank or omitted, and can override the underlying CodeSystem status.
  • ValueSet entries without a status continue to load as standard codes.

• Bug Fixes

  • Code activity validation now correctly honors ValueSet membership status when determining whether a code is active.

[coderabbitai]

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title is concise and accurately summarizes the main change: reading terminology value-set membership status.
Description check	✅ Passed	The PR description follows the template and includes changes, testing, unit tests, and documentation notes.

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