dotnet: PostgresLogStore — first per-domain analytics impl on PG (HOL-29)

[BrewingCoder]

Summary

First Postgres-backed implementation of HoldFast.Analytics.ILogStore. Mirrors ClickHouseService's six log methods with backend-equivalent semantics — same cursor format, same query-filter shape, same pagination pattern. Sets the implementation pattern for HOL-30..33.

What this PR adds

• analytics.logs table (migration 0010) — TimescaleDB hypertable with daily chunks + 30-day drop_chunks retention policy. Conditional via pg_extension lookup so it degrades to a regular table if TimescaleDB isn't installed.
• analytics.log_keys / analytics.log_key_values catalogs (migration 0011) — inline-upserted from PostgresLogStore.WriteLogsAsync rather than maintained by a materialized view (CH used SummingMergeTree + MV). Immediate consistency, no refresh policy. Future PR can swap to TimescaleDB continuous aggregates if write volume warrants.
• PostgresLogStore.cs — direct Npgsql, no EF Core on the high-volume insert path. Bulk inserts via NpgsqlBinaryImporter (binary COPY).
• Per-domain DI swap in Program.cs: Storage:Analytics:LogStore = postgres binds ILogStore to PostgresLogStore; default stays ClickHouse. Per-store granularity (rather than the single-knob Storage:Analytics planned for HOL-34) lets each impl land + be verified independently across HOL-29..33.

Behavior parity with CH impl

• Cursor encoding/decoding via HoldFast.Analytics.CursorHelper — cursors round-trip across backend switches
• CountLogsAsync returns 0L (matches CH stub; both backends will get a real impl together)
• ReadLogsHistogramAsync buckets by severity_text over N=48 equal-width time slices
• query filter: body ILIKE %q% OR log_attributes->>'service_name' ILIKE %q% (CH does the same map-key lookup; PG uses JSONB ->>)

Test plan

• dotnet build -c Release — 0 errors / 0 new warnings
• dotnet test — 3,079 pass (was 3,061; +18 new)
  • 14 unit tests for ClampLimit + DateOnlyOf edge cases (negative limits, overflow, mixed DateTimeKind, default sentinels)
  • 4 live integration tests against localhost:5432, gated [Trait("Category","PgIntegration")] + Skip.IfNot so CI without a DB sidecar passes:
    • WriteLogs + ReadLogs round-trip with JSONB attributes — body, severity, service info, attribute dictionary all survive the binary-COPY → query path
    • log_keys / log_key_values populated correctly — distinct values per key match expected
    • Empty/null attributes don't crash inline upsert — defensive null-handling on LogAttributes
    • Counts aggregate across batches via ON CONFLICT DO UPDATE — verified 3+2+1=6 across two WriteLogs calls
• Migrations applied cleanly to the running timescale/timescaledb-ha:pg16 container — analytics.logs is a hypertable per timescaledb_information.hypertables

Out of scope

• The DI swap is per-domain; HOL-34 will consolidate to Storage:Analytics = ClickHouse | Postgres once HOL-30..33 land
• Smoke ingest with Storage:Analytics:LogStore=postgres set on the running backend image — the integration tests prove the impl works against live PG; full end-to-end via the OTLP ingest pipeline waits until HOL-34's image-level switch

Stats

7 files changed, +1023 / -5.

Closes HOL-29. Second story of the Postgres-backend EPIC (HOL-28).

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