Split AlertNotebookEndpoint's authored templates into per-family files (#4223)

[erikdarlingdata]

Refs #4223.

Why

AlertNotebookEndpoint held every authored notebook template (Blocking, Deadlocks) in one 842-line file, with a metric-name if-chain choosing between them. Splitting each family into its own file, and turning the if-chain into a single sorted registration table, means future template families can be built in parallel, each touching only its own file plus one new line in the table.

What changes

• AlertNotebookEndpoint.cs (core): internal static class becomes internal static partial class. The metric-name if-chain in AuthoredTemplate is replaced by a static readonly array s_authoredTemplates of (string[] Metrics, AuthoredTemplateEntry Entry), one row per family, sorted case-insensitively by each row's first metric name. AuthoredTemplate now looks up the table instead of branching. Made internal (was private) so a test pin can check the table directly.
• New AlertNotebookEndpoint.Templates.Blocking.cs: BlockingTemplateVersion and BuildBlockingCells, moved verbatim.
• New AlertNotebookEndpoint.Templates.Deadlocks.cs: DeadlocksTemplateVersion and BuildDeadlockCells, moved verbatim.
• Shared helpers (HeaderCell, StatusCell, ReadCell, AuthoredReadCell, TimelinePanel, RankedPanel, etc.) stay in the core file, since both families use them.

No behaviour change. Line endings (CRLF) and file header match the original.

Test plan

• Byte-identical before/after: a temporary in-process test (not committed) serialized the bound notebook-definition JSON for "Blocking Detected", "Blocking Wait Time", "Deadlocks Detected", and one mechanical metric ("High CPU") against a fixed alert row and window, once before the move and once after. diff between the two captures reports no differences.
• New pin (AlertNotebookAuthoredTemplateTests.cs): RegistrationTable_EveryFamilyResolvesAndValidates walks every row of s_authoredTemplates, checks every metric name resolves to a non-null entry with a unique id, and runs each entry's built cells through DarlingWebEndpoints.ValidateNotebookDefinition. RegistrationTable_IsSortedByFirstMetricName pins the table's sort order.
  • RED on the pre-fix code: s_authoredTemplates doesn't exist there, so this is a compile failure against origin/dev, not a runtime failure.
• Existing pins, run in-process on macOS (Darling.Tests.dll, Microsoft.WindowsDesktop.App removed from its runtimeconfig for this run only): AlertNotebookAuthoredTemplateTests, AlertNotebookEndpointTests, DocCommentHygieneTests. All 126 tests pass, 0 failed.
• Build: Darling.Tests.csproj and Lite.Tests.csproj both build 0 errors with -p:EnableWindowsTargeting=true. Neither test project runs live PostgreSQL classes (no live-DB pins touched by this change).

CHANGELOG entry

None: a structural move with no behaviour change.