Manual test pass: PostgreSQL backend

[smunini]

Summary

Run the manual testing pass in MANUAL_TESTING_MATRIX.md for the PostgreSQL backend (HFS_STORAGE_BACKEND=postgres) and record the results in this issue.

The matrix is organised backend-first: every backend gets the same T0 through T8 sequence. This issue covers one row of that matrix.

Procedure

Follow MANUAL_TESTING_MATRIX.md sections 2 through 12 in order, using the postgres row of the per-backend environment table in section 5.

Infrastructure: start PostgreSQL 16 per section 4 (docker run ... postgres:16).

• T0 Build with the CI selection: cargo build --workspace --all-features --release
• T1 Start HFS with HFS_STORAGE_BACKEND=postgres HFS_DATABASE_URL=postgresql://helios:helios@localhost:5432/helios and confirm /health, /metadata, and /ui
• T2 Import at least 10,000 resources from the Synthea bulk_1k archive (record wall-clock time, bundle count, resource total)
• T3 One search per type: string, token, date, number, quantity, reference, uri, composite, special, plus chained, reverse-chained, _include/_revinclude, _sort, paging, _content, POST search
• T4 Bulk Data $export: system, patient, group; all three NDJSON format spellings; unsupported format returns 400; UI /ui/bulk-export
• T5 Create a ViewDefinition via API and via /ui/sql/view-definitions; examine $sql-run output in json, csv, ndjson, parquet
• T6 $sql-export with a ViewDefinition subject, a SQLQuery Library subject, and a SQLView Library subject, cycling all four formats; UI /ui/sql/export
• T7 Create a SubscriptionTopic (R4 backport Basic) and rest-hook Subscription, trigger notifications, verify delivery, $status, $events
• T8 Verify the /ui/subscriptions activity dashboard (cards, table row, sparkline, failure streak, rehydration after restart)

Results to attach

• The filled-in postgres row of the matrix table from section 1 of MANUAL_TESTING_MATRIX.md
• build.log tail, hfs-postgres.log, import-postgres.log, and the T2 timing line
• One T4 manifest and one T6 result manifest
• Screenshots of /ui after import, /ui/sql/export with a completed card, and /ui/subscriptions after T8
• For any failure: the request, the OperationOutcome, the log excerpt, and a link to the issue filed for it

Acceptance criteria

• Every T0 through T8 cell for the postgres row is marked pass, or marked fail with a linked issue, or marked N/A where section 1's expected-support table says the capability is unsupported on this backend
• Results and artifacts listed above are attached to this issue