chore(agent): track .agent/ planning tree in git

Remove the blanket .agent/ gitignore so the phase roadmap, user
stories, reports, and PLAN.md are versioned with the code. Only
runtime artifacts (.agent/phase-sessions/, .agent/pipeline.log)
remain ignored. Update AGENTS.md git protocol rule to match.

.agent/user_stories/chat-persistence.md

@@ -0,0 +1,45 @@
+# Story: Chat Survives a Refresh (localStorage)
+
+**Phase:** `14_chat_persistence.md` · **E2E:** `tests/e2e/test_chat_persistence.py`
+
+## Narrative
+
+As **a user**, I want my conversation to **survive a browser refresh**
+and a trip to another page — the previous session should be waiting for
+me when I come back.
+
+- **Given** I have asked a few questions
+- **When** I refresh the page (or go to Sources and come back)
+- **Then** the whole conversation is restored: my questions, Brain's
+  answers (rendered markdown), the source chips, and deflected answers
+  with their "Maybe try" chips — amber style included.
+
+## Acceptance criteria
+1. Conversation state (user + brain messages, with sources/deflection/
+   suggestions metadata) is stored in `localStorage` under a versioned
+   key; user messages are saved when sent, brain answers when the turn
+   completes.
+2. On load, stored messages are re-rendered (markdown, source chips,
+   deflected styling + maybe-try chips); the empty state is hidden when
+   a conversation exists.
+3. "New chat" control (chat header) clears the stored conversation and
+   returns to the empty state with suggestions.
+4. Storage failures (private mode / quota) degrade silently — chat still
+   works, nothing throws.
+5. Size-bounded: oldest messages are dropped if the serialized
+   conversation outgrows the quota budget.
+6. Unit + integration green, `app/` coverage >90%, story E2E green in
+   isolation, one `--no-gpg-sign` commit.
+
+## Playwright Mapping Rule
+**Test Scenario → `tests/e2e/test_chat_persistence.py`** (mock LLM, seeded KB):
+1. `test_conversation_survives_reload` — ask → answer with source chip →
+   `page.reload()` → both bubbles restored (text + chip href), empty
+   state hidden.
+2. `test_deflected_turn_restores_styling` — off-topic question →
+   deflected answer → reload → amber bubble + "Maybe try" chips back.
+3. `test_new_chat_clears_conversation` — with a conversation, "New
+   chat" → messages gone, empty state + suggestions back, storage key
+   cleared.
+4. `test_persists_across_page_navigation` — ask → go to Sources → back
+   to `/` → conversation still there.