feat(pegas-memory): Tier-1 self-improvement tools (commit + staleness)

- memory_commit: closes the 'commit hole' — writes verified answers from
  closed gaps back into atoms (mandatory dedup); leaves gap open if no
  verified answer exists. Reads verified status from PostgreSQL (source of
  truth), not the Qdrant projection.
- memory_stale: staleness guard with two signals — content-staleness
  (re-fetch + LLM verdict, needs proxy for foreign sites) and age-staleness
  (proxy-free fallback by pm_document.fetched_at, max_age_days).
- db: populate pm_document.fetched_at on upsert (freshness signal).
- docs: README/AGENTS/ARCHITECTURE/EXAMPLES updated (18 tools).
- self_improve.py: new module (227 lines).

pegas_memory/db.py

@@ -30,8 +30,8 @@ def upsert_document(conn, *, kind: str, uri: str | None, title: str | None,
             if row:
                 return row["id"]
         cur.execute(
-            """INSERT INTO pm_document (kind, uri, title, content_hash, authority, meta)
-               VALUES (%s, %s, %s, %s, %s, %s)
+            """INSERT INTO pm_document (kind, uri, title, content_hash, authority, meta, fetched_at)
+               VALUES (%s, %s, %s, %s, %s, %s, now())
                ON CONFLICT (uri) DO UPDATE SET title = EXCLUDED.title
                RETURNING id""",
             (kind, uri, title, content_hash, authority, json.dumps(meta or {}, ensure_ascii=False)),