Plan analysis: the store readers fill ServerMetadata's cost threshold, max server memory and database settings (#4597)

[erikdarlingdata]

Refs #4597. #4601 is merged; this is now against dev. Part of #4511.

What changes

ServerMetadata gains PerformanceStudio's DatabaseMetadata (name, compatibility level, collation, RCSI, the auto-stats flags, forced parameterization) and ScopedConfigItem shapes, plus a Database property. Both store readers — DarlingServerMetadataReader (Postgres) and Lite's LocalDataService.GetServerMetadataForPlanAnalysisAsync (DuckDB) — now also read cost threshold for parallelism and max server memory (MB) from the config history, and, when a database name is given, the newest database_config/v_database_config row for that database. A missing or absent database row leaves Database null rather than failing the read, the same non-fatal contract the existing edition/MAXDOP read already has.

The viewer's plan-opening entry points (ProcedureHistoryWindow, QueryStatsHistoryWindow, QueryStoreHistoryWindow, WaitDrillDownWindow, ViewerActualPlanFlow, ViewerServerTab.Plans, ViewerDataService) and the drill-down/MCP paths (PgDrillDownCollector.Plans, DarlingMcpPlanTools) now pass the database name through to the reader wherever the call site already has it (a plan opened from a database-scoped history window or drill-down); sites with no database context at hand (a pasted plan, a plan looked up by hash alone) still call the reader with no database name, same as before, and get everything except Database.

PerformanceStudio parity

PM fills every DatabaseMetadata member PS's live fetch fills from sys.databases, sourced from PM's collected database_config/v_database_config row instead of a live connection (Darling has no live session at these call sites — same reasoning the existing edition/MAXDOP read already documents). ScopedConfigItem/NonDefaultScopedConfigs is added to the model to keep the shape aligned with PS, but nothing populates it yet in this change; no reader queries database_scoped_config here. That's the remaining PS surface with no PM data behind it yet.

Test plan

• dotnet build Darling/Darling.Tests/Darling.Tests.csproj -c Release -p:EnableWindowsTargeting=true: 0 warnings, 0 errors.
• Live (own rig, TimescaleDB Postgres container): PlanSync4597ServerContextFieldsLiveTests, PlanSync4530ReaderLiveTests, PlanSync4530DrillDownLiveTests → 4/4/… all green, Total: 20 across those plus StorageCommandTimeoutTests, 0 failed.
• Census family + StorageCommandTimeoutTests + LivePostgresCollectionHygieneTests + LiveCleanupConversionRatchetTests + DocCommentHygieneTests + CommentFilterAdoptionTests + McpPayloadContractCensusTests + McpToolsListBudgetTests: Total 204, Failed: 1 — LivePostgresCollectionHygieneTests.EveryClassUsingTheSharedStore_IsSerializedOrDocumentsWhyNot fails on this Mac only, with Could not load file or assembly 'PresentationFramework'; that's a WPF type load unavailable on macOS, not a regression (confirmed unrelated to this change by running it before and after).
• RED: changed the new database_config predicate to database_name = 'red-mutation', rebuilt, reran PlanSync4597ServerContextFieldsLiveTests → Assert.NotNull() Failure: Value is null at the seeded-database assertion. Reverted, rebuilt, reran → green again (Total: 20, 0 failed).
• StorageCommandTimeoutTests initially caught one real gap: the new database_config read's NpgsqlCommand had no explicit deadline. Fixed by setting CommandTimeout = StorageCommandDeadlines.McpReadSeconds (this reader serves the MCP plan tools and drill-downs, the same regime as the file's other MCP-facing reads).
• Lite: dotnet build Lite/PerformanceMonitorLite.csproj, Lite.Tests/Lite.Tests.csproj, Darling/PerformanceMonitor.Darling.Viewer, Darling/PerformanceMonitor.Darling.Service (all -p:EnableWindowsTargeting=true) → 0 warnings, 0 errors on all four.
  • Added a source census in PlanSync4597ServerContextFieldsLiveTests confirming Lite's PlanServerMetadataSql names the same v_database_config columns Darling's database_config schema does.
  • Added Lite.Tests/PlanServerMetadataDatabaseArgTests.cs (a new file, not the sibling PlanServerMetadataReaderTests.cs, which Plan analysis: rule 38 reads the server's edition and MAXDOP at every entry point (#4530) #4601 also edits) with three build-only pins for the database argument, copying that file's SharedDuckDbFixture setup pattern and filling every NOT NULL column of server_properties and database_config. Can't run on macOS (Lite.Tests discovery dies on WindowsBase); CI decides them.
  • No ProjectReference or lock-file changes in this branch, so no dotnet restore --force-evaluate was needed.

CHANGELOG

SECTION: None
ENTRY: None: the fields feed the Server Context card (#4597), a separate PR