P4: contrib/store — persona SQLite store (JSON-blob round-trip)

db.Personas() satisfies persona.Storage over SQLite. Each Agent is stored as a
JSON blob with extracted indexed columns (owner_id, name, webhook_secret,
chatbot_channel_filter, schedule, next_run_at) — so the WHOLE struct round-trips
(no domain<->GORM<->DB field-loss footgun) while the lookups stay indexable.

Test proves the round-trip preserves nested + map fields (SkillPalette,
StateReactEmoji), the owner/name + webhook + chatbot-filter queries, the
scheduled-due query, and MarkAgentScheduledRun clearing the due window.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -76,8 +76,9 @@ BATTERIES (opt-in siblings, each nil-safe + a default):
              BudgetStorage iface + Memory default
 
 contrib/store/   SECOND module (+ modernc.org/sqlite):   [P4 ~]
-  pure-Go SQLite impls of the *Store seams. budget ✓
-  (conformance-tested); persona/skill/audit pending.
+  pure-Go SQLite impls of the *Store seams. budget +
+  persona ✓ (JSON-blob+indexed cols, round-trip tested);
+  skill/audit pending.
   CI proves the driver lands HERE, not in the core go.sum.
 ```