feat(trace): persist per-prompt traces to SQLite + query API

[a-yeyang]

Summary

Per-prompt agent traces (previously written only to .siclaw/traces/*.json) are
now also persisted to a local SQLite DB, with a Gateway-served query API. Enables
cross-session retrospective and slow-task audits without scanning files.

What's added

• .siclaw/traces.sqlite — standalone node:sqlite store (lazy-loaded; on
  Node <22.13 without --experimental-sqlite, gracefully degrades to file-only).
• Schema: INTEGER PRIMARY KEY AUTOINCREMENT clustered id +
  trace_key TEXT UNIQUE (business key, matches the on-disk filename stem).
  Beijing-time TEXT columns started_at / ended_at / created_at
  (YYYY-MM-DD HH:mm:ss.SSS). Indexes on (user_id, started_at),
  (started_at), (session_id, prompt_idx).
• Auto-migrations via PRAGMA user_version (v1 → v2 → v3), in-place,
  preserves all existing rows.
• Query API on Gateway (:3000, eager-start — no AgentBox spawn needed):
  • GET /api/traces — filters: username, userId, lastHours, lastDays,
    from, to, minDurationMs, outcome, limit. Keyset pagination via
    cursorStartedAt + cursorId.
  • GET /api/traces/:traceKey — full JSON body (byte-identical to disk file).

Usage

# Slow tasks (>60s) in the last 3 hours
curl 'http://localhost:3000/api/traces?lastHours=3&minDurationMs=60000' | jq

# Full body for one trace
curl 'http://localhost:3000/api/traces/trace-20260422-11-07-57-admin' | jq