refactor(agents): migrate .agent/ planning tree to .agents/

Standardize on the .agents/ directory (shared with project skills):
phases/, user_stories/, reports/, screenshots/, validate.sh, and
phase-sessions/ + pipeline.log all move to .agents/ (git mv preserves
history; runtime artifacts move alongside).

Updates every reference in AGENTS.md, README.md, .gitignore, app
docstrings, and test story headers. Historical KB content in data/
and the runtime pipeline.log transcript are left untouched.

.agents/phases/complete/27_global_tuning/00_phase.md

@@ -0,0 +1,44 @@
+# Phase 27 — Global Tuning Manager
+
+**Source:** `TODO.md L3 — "Add a way to add 'global tuning' without having a chat to reply to. Also previous tunes should be editable."`
+**Story:** `.agents/user_stories/global-tuning.md`
+**Context:** Phase 15 added steering notes (owner instructions injected into every system prompt as the `<tuning>` section); phase 16 gated the whole `/api/steering` router behind `require_admin`. The current UI only lets the admin **create** a note by pressing "Tune" under a completed chat bubble, and the header "Tuning" panel lists notes newest-first with **delete-only** per note. There is no way to add a note without a chat, and no way to edit an existing one.
+
+## Objective
+Give the admin a **Global Tuning** page (`/tuning.html`) where notes can be created, **edited**, listed, and deleted **without any chat conversation** — and expose it via an admin-only header button. Add a `PUT /api/steering/{note_id}` endpoint for updates. The existing chat-page "Tune" button and header panel keep working (create + delete) so nothing regresses.
+
+## Dependencies
+- `15_steering_notes` (complete) — the `steering_notes` table, the `<tuning>` prompt section, the `/api/steering` router (list/create/delete), and the chat-page "Tune" button + header panel this phase augments.
+- `16_admin_auth` (complete) — `require_admin` + the signed-cookie auth; the tuning page is admin-only, following the same gate pattern as the Sources page.
+- `19_shared_header` (complete) — the shared header bar that gains the admin-only "Tuning" link.
+
+## Tasks
+1. `01_steering_put_endpoint.md` — add `PUT /api/steering/{note_id}` (update a note; 404 unknown, 422 invalid) + `PATCH`-friendly schema in `app/schemas.py`
+2. `02_tuning_page_html_css.md` — create `frontend/tuning.html` (title, note list, create form, edit-in-place) + CSS
+3. `03_tuning_js_crud.md` — create `frontend/assets/tuning.js` with full CRUD (list, create, edit, cancel, delete) + live announcer
+4. `04_header_button_and_e2e.md` — add the admin-only "Tuning" header button → `/tuning.html`; E2E suite for the tuning page
+
+## Testing & Quality
+- Unit/integration: `PUT /api/steering/{note_id}` (admin 200, anon 403, unknown 404, invalid 422) — unit + integration.
+- Coverage: **>90%** on `app/` (new endpoint + schema).
+- E2E: `tests/e2e/test_global_tuning.py` — the story gate, run in isolation.
+
+## Completion Criteria
+- [ ] Admin can open `/tuning.html` (via the header button) and create a note without any chat; the note appears in the list and steers future answers (verifiable via the chat page after a turn, or via the list).
+- [ ] Admin can **edit** an existing note inline (edit button → textarea pre-filled → Save → updated text); the change is reflected in the list and in the `<tuning>` prompt (integration test).
+- [ ] Delete still works; create-then-edit-then-delete round-trips cleanly.
+- [ ] Anonymous users get 403 on `/tuning.html`'s data and on `PUT /api/steering/…`; the header "Tuning" link is hidden for anonymous.
+- [ ] The chat-page "Tune" button and header panel are unchanged (create + delete still work).
+- [ ] `uv run pytest` green; `uv run pytest --cov=app --cov-report=term-missing` TOTAL ≥ pre-change number.
+- [ ] `uv run pytest tests/e2e/test_global_tuning.py -v --no-cov` green in isolation.
+- [ ] `uv run ruff check . && uv run pyright` clean.
+- [ ] UI Structure Check (AGENTS.md rule 5): tuning page — landmarks, labeled controls, contrast ≥4.5:1, focus-visible, ≥44px targets, centered column, no CDN.
+- [ ] `.agents/user_stories/global-tuning.md` exists.
+- [ ] One `--no-gpg-sign` commit staging only this phase's files; `.agents/phases/todo/27_global_tuning/` moved to `.agents/phases/complete/`.
+
+## Locked decisions
+- **A10 untouched** — `PUT /api/steering/{note_id}` is a new stateless route under `/api`; the API stays stateless, admin-only via `require_admin` (the existing gate).
+- **A11 untouched** — vanilla HTML/CSS/JS, no CDN, no new packages, system font stack; the tuning page is a new page + new module script.
+- **No schema change / no migration** — the `steering_notes` table already stores `note`; `PUT` updates the existing `note` column (A13 untouched).
+- **A16 honoured** — one new story E2E suite + adapted regressions.
+- **A17 honoured** — one atomic `--no-gpg-sign` commit.