feat(littleblue): agent seed + persona + chat route

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/db/migrations/017_little_blue.sql

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+-- Seed Little Blue, the homelab caretaker/fix-it agent. read + act (no content write).
+-- 'act' is enforced by the action service's tier-gating + whitelist, not canAct.
+INSERT INTO agents (slug, name, kind, model, capabilities)
+VALUES ('little-blue', 'Little Blue', 'claude', NULL, '{"read":true,"act":true}'::jsonb)
+ON CONFLICT (slug) DO NOTHING;