Add SQLite-backed persistent history, replay windowing, and 4 new rea…

[Fayupable]

…d-only insights

• Replace the in-memory ring buffer with a SQLite-backed history store (WAL mode, auto_vacuum, redacted query text, age/count/disk-size-based pruning) so replay survives a restart
• Recording now follows monitoring automatically instead of a separate time-capped start/stop action; replay window is selectable (1h-24h) with periodic-snapshot downsampling
• Add prepared transaction, replication slot, long-running query, and unlogged table checks to Insights, plus temp file rate to the live dashboard stats
• Add table-driven unit tests for every domain file with real decision logic (previously untested)
• Fix a raw-query-text exposure gap in the new long-running-query collector to match the existing pg_stat_statements-only convention

What does this PR do

Why

How was this tested

• go build ./... && go vet ./... && go test ./... passes
• npx tsc -b passes (if frontend changed)
• Manually tested in the browser (describe what you clicked through, if UI changed)

Checklist

• New backend code follows the hexagonal architecture rules in CONTRIBUTING.md (no SQL outside infrastructure/postgres, no Postgres vocabulary in domain)
• Any new Insights category's SQL filter/order matches the domain layer's actual judgment criteria (see CONTRIBUTING.md's note on this recurring bug class)
• This does not add any capability beyond read-only SELECT against statistics views