issue-3653 A8 option B: WindowTiles shared tile helpers (lane L1c)

[erikdarlingdata]

Part of #3653 (A8 option B, lane L1c)

What

Adds PerformanceMonitor.Analysis.Baselines.WindowTiles, the shared per-hour tile helpers every detector call site (24 of them, across the SQL Server store, the PostgreSQL target and Lite's DuckDB — design §2) will call. Per the brief, this lane touches only two new files:

• PerformanceMonitor.Analysis/Baselines/WindowTiles.cs
• Darling/Darling.Tests/WindowTilesTests.cs

WindowTiles provides:

1. LocalHourSql — the tile-key SQL const (date_trunc('hour', BaselineLocalClock.LocalCollectionTimeSql)), documented to bind $4..$6 from BaselineBucketMap.WindowClock, never the cached baseline clock.
2. WholeWindow(IReadOnlyList<WindowTile>) — the whole-window aggregate the never-blind fallback feeds to today's EvaluateZScore. Peak = max; Mean = samples-weighted mean; Samples = sum; PeakTimeUtc = the max-peak tile's, later tile wins a tie; LocalHour = earliest tile's. Empty list or ΣSamples = 0 → default with Samples 0.
3. LocalHourToUtc(DateTime, LocalClockWindow) — inverts LocalCollectionTimeSql: tries local − OffsetBeforeMinutes, accepts it if before TransitionAtUtc, else falls back to local − OffsetAfterMinutes. A repeated (fall-back) local hour maps to its FIRST occurrence, since the before-candidate is tried first.
4. AddTileMetadata(...) — adds exactly the 7 new fired-fact keys the design's §1 lists (tile_local_hour, tile_day_of_week, tile_start_ticks, tiles_scored, tiles_fired, window_peak, window_samples_total). Does not touch the existing peak_*/baseline_*/deviation_sigma keys — those stay the detectors' job.
5. ReadTile(IDataRecord, ...) — builds one WindowTile from a row, tolerant of DBNull peak/mean/samples (→ 0) and a negative/DBNull peak-time ordinal (→ null). Uses Convert.ToDouble/Convert.ToInt64 so it works against both NpgsqlDataReader and DuckDBDataReader.

TileVerdict and WindowTile already existed from #4166 (lane L1a); this lane only consumes them.

Tests added (all in Darling.Tests.WindowTilesTests)

• LocalHourSql_Contains_LocalCollectionTimeSql_Verbatim
• WholeWindow_WeightedMean_And_MaxPeak_LaterTileWinsTie
• WholeWindow_EmptyList_ReturnsDefault_ZeroSamples
• WholeWindow_AllTilesZeroSamples_ReturnsDefault_ZeroSamples
• LocalHourToUtc_FixedOffset_MapsLocalToUtc
• LocalHourToUtc_SpringForward_MapsBothSidesOfTheTransition
• LocalHourToUtc_FallBack_AmbiguousHourMapsToFirstOccurrence
• AddTileMetadata_AddsExactlySevenKeys
• ReadTile_ReadsAllColumns_WhenPresent
• ReadTile_DBNullCells_BecomeZeroOrNoPeakTime
• ReadTile_NegativePeakTimeOrdinal_MeansNoPeakTime

Verification

• dotnet build green for PerformanceMonitor.Analysis, Darling/Darling.Tests (both with -p:EnableWindowsTargeting=true) and Lite/PerformanceMonitorLite.csproj (confirms the helper compiles for Lite too).
• Targeted runs (macOS, Microsoft.WindowsDesktop.App stripped from the test runtimeconfig for the run only, then restored): *WindowTiles* (11/11), *AnomalyGateTiles* (12/12), *DocCommentHygiene* (77/77), *LocalClock* → LocalClockBucketKeyTests (13/13). All green.
• Full Darling suite once, DARLING_TEST_PG unset: Total: 13657, Errors: 0, Failed: 214, Skipped: 727, Not Run: 2. All 214 failures are the pre-existing Windows-only set the brief names (WPF/registry/Windows-service-install classes — ViewerChartContextMenuTests, DarlingInstallLocationTests, TargetProviderTests, BulkServerOnboardingMappingTests, etc.) — none are new, none touch WindowTiles, AnomalyGate, or BaselineBucketMap.
• scrubcheck on the diff: 0 hits.

Not verified

• No live PostgreSQL test needed per the brief (none added; WindowTiles has no store dependency).
• The 24 detector call sites are NOT wired to WindowTiles in this lane — that is later lanes' work per the design's §2 inventory.

Base

Based on origin/feat/3653-b-tile-gate (PR #4166 was still open at start; WindowTile and TileVerdict came from it) rather than dev, per the brief's stacking rule.

CHANGELOG entry

None (per brief).

Coordinator verification (head fd91b4d)

• The core file was read. WindowTiles.cs matches the lane-L1c brief.
• LocalHourToUtc was checked by hand against both DST cases:
  • spring-forward: local 01:00 → 06:00Z, local 03:00 → 07:00Z;
  • fall-back: local 01:00 → 05:00Z (the first occurrence), local 02:00 → 07:00Z.
• Classes run: *WindowTiles* 11/11, *AnomalyGate* 23/23, *DocCommentHygiene* 77/77, *LocalClock* 13 passed with 1 live skip.
• Builds: Lite/ builds with the new helper, with 0 errors.
• Full Darling suite without PG, on macOS: 13657 total, 214 failed. The failure set is identical to dev's Windows-only set.
• Rebased onto dev after issue-3653 A8 option B: the per-hour tile gate and its math (lane L1a) #4166 merged (82abf48). The head is now adad1b9, with the same two files. The build is green after the rebase.