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/user_stories/configurable-brand.md

@@ -0,0 +1,51 @@
+# Story: Configurable app name
+
+**Phase:** `39_configurable_brand` · **E2E:** `tests/e2e/test_configurable_brand.py`
+
+## Narrative
+
+As **the owner**, the app is "Brain of Reese" because that's what I named
+it — but the name is hard-coded across every template and JS string. I want
+to be able to **rename the app with one env var** (`BOR_APP_NAME`) so every
+page title, the header brand, the status labels, and the aria text carry
+the new name without touching code.
+
+- **Given** the app is running with `BOR_APP_NAME="Brain of Testy"`
+- **When** I open any page (chat, sources, tuning, login, document viewer)
+- **Then** the title, the header brand, the status labels
+  ("Brain of Testy is thinking"), the empty-state greeting, and the
+  document-viewer titles all say "Brain of Testy" — and with the variable
+  unset the app is byte-identical to today ("Brain of Reese").
+
+## Acceptance criteria
+1. `GET /api/config` (public, stateless) → `{app_name, version}` from
+   settings — exactly those two keys (no secrets, no other settings);
+   unit + integration tested.
+2. `frontend/assets/brand.js` (classic script, loaded first on all five
+   pages): sets `window.BOR_BRAND` synchronously (default "Brain of
+   Reese"), fetches `/api/config` (`cache: "no-store"`), and applies the
+   name — `document.title` (global replace of the literal), every
+   `.brand-text` (bold split: a name starting "Brain of " bolds the
+   remainder, else plain; the name is HTML-escaped), every text node and
+   the `aria-label` / `placeholder` / meta-`content` attributes containing
+   the literal; a fetch failure falls back to the default (console.warn,
+   the page never breaks).
+3. The JS hard-codes move off the literal: `app.js` (status labels, the
+   typing label, the elapsed-hint aria) + `document.js` (page titles) read
+   `window.BOR_BRAND` (default "Brain of Reese" if unset).
+4. `Containerfile`: an esbuild line for brand.js next to the others.
+5. The story E2E boots its **own** app instance with `BOR_APP_NAME`
+   overridden (distinct port; the shared conftest server keeps the default
+   name so the existing title assertions stay green) and asserts
+   title/brand/greeting/aria/label.
+6. `.env.example` + README document `BOR_APP_NAME` (what it affects, the
+   default, the bold-split rule).
+7. Unit + integration green, `app/` coverage >90%, story E2E green in
+   isolation, ruff + pyright clean, one `--no-gpg-sign` commit.
+
+## Playwright Mapping Rule
+`tests/e2e/test_configurable_brand.py` — one story, one file, run in
+isolation: the overridden-name instance shows the new brand in the title,
+the header `.brand-text` (with the bold split), the empty-state greeting,
+the messages aria-label, and the chat status label; the default-name
+shared server still renders "Brain of Reese" (the no-op regression).