Crow personas and generated banter

- personas.go: backstory, prompt policy and output policy per crow;
  Hugin and Munin grounded in Grimnismal 20 and Gylfaginning 38;
  every working crow also follows a common output policy
- Personas go into each crow's instructions; Sentry keeps JSON-only
- banter.go: retrieve backstory, relationships and recent flock
  memory, then the speaking crow generates one line in character;
  max 2 per list against the list budget, never blocks work,
  unusable lines dropped
- crow.banter event, GET /api/crows, `crows personas` -> PERSONAS.md
- UI: epithets on tiles and messages, banter as quiet asides

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UQnSw4RRWp8uqpj3nsnnXF

EVENTS.md

@@ -58,3 +58,15 @@ Guardrails: name 1–40 characters after trimming; `nest_id` is a slug of the na
 Event changes:
 - `list.started` adds `nest_id`.
 - `crow.flying` adds `borrowed` (bool): true when the crow is not in the nest's core. Always false for Sentry, Elder, and the `todo` nest.
+
+## Personas and banter
+
+| Method | Path | Returns |
+|---|---|---|
+| GET | `/api/crows` | `[{"name", "epithet", "strength", "backstory"}]` for all ten crows |
+
+| Event | Payload (besides list_id, ts) | Meaning |
+|---|---|---|
+| `crow.banter` | `item_id`, `crow` (speaker), `to` (the crow it's addressed to), `text` (one line) | A generated aside between crows. Not part of any answer. |
+
+Banter is generated: the server retrieves the involved crows' backstories, their relationship and recent flock events, then the speaking crow writes one line in character. At most 2 per list, counted against the list budget; banter never blocks work, and a failed or unusable line is dropped. `list.finished` waits up to 20 seconds for in-flight banter. See `PERSONAS.md`.