Add CLAUDE.md and docs/widgets.md; fix stale single-mode architecture docs

Repo-tracked context so a fresh Claude Code session (this machine or a
remote/cloud one) gets accurate project context without relying on this
session's local, machine-specific memory: repo conventions (no
co-author trailers, flag copyleft deps explicitly, scope security
gates broadly -- each backed by a real past incident), testing/deploy
workflow, and pointers into the existing docs.

docs/architecture.md's sequence diagram and boot-flow text still
described the pre-widget-system single-photo-queue model (e.g. "force-
advance to next queued photo") even though that was fully replaced by
the widget system across this branch's recent history -- fixed, and
added docs/widgets.md distilling the widget system's actual design
(data model, grid placement, compositor, button-action dispatch) as
current-state documentation, including the still-open Phase 6 cleanup
(legacy Frame columns not yet dropped) as a known gap.

CLAUDE.md

@@ -0,0 +1,71 @@
+# espresso_frame
+
+A DIY e-ink photo frame: an ESP32-C6 (`firmware/`, ESP-IDF) driving a
+Waveshare 7.3" E Ink Spectra 6 panel (800x480, 6-color, SPI), paired with a
+self-hosted FastAPI server (`server/`) that pulls from Immich, does all
+image processing (crop/dither/quantize/pack), and serves a placeable
+photos/calendar/whiteboard widget system to the device.
+
+Start here, don't re-derive from scratch:
+- [`docs/architecture.md`](docs/architecture.md) -- how firmware and
+  server talk (sequence diagram, boot flow).
+- [`docs/widgets.md`](docs/widgets.md) -- the server-side widget system
+  (data model, grid placement, compositor, button-action dispatch). Notes
+  a known gap at the bottom (legacy `Frame` columns not yet dropped).
+- [`docs/hardware.md`](docs/hardware.md) -- wiring.
+- [`server/README.md`](server/README.md), [`firmware/README.md`](firmware/README.md)
+  -- per-component setup, config, and a lot of accumulated gotchas
+  (Immich API shape, TLS trust-anchor details, button GPIO wakeup
+  quirks, etc.) -- check these before assuming something is a new bug.
+
+## Conventions specific to this repo
+
+- **No `Co-Authored-By: Claude` trailers in commits.** Attribution lives
+  in the root [`README.md`](README.md) instead (see its last line) --
+  the maintainer's explicit preference, not the default.
+- **Copyleft dependencies need an explicit flag, not a silent decision.**
+  Before adding anything LGPL/GPL/AGPL (or unclear), verify the actual
+  license via `pip show`/package metadata -- including transitive deps,
+  not just the top-level package -- and present the finding and tradeoff
+  in plain text rather than picking an approach unilaterally (hand-rolling
+  an alternative, swapping packages, silently accepting it). This project
+  has knowingly accepted AGPL-3.0-or-later exposure once already
+  (`icalendar-searcher`, a transitive dep of `caldav`) as a deliberate,
+  explicit call -- not a precedent for skipping the check next time.
+- **Scope new auth/access-control broadly, not just to the literal
+  endpoint named.** When a request changes the trust model (e.g. adding
+  public-internet exposure), apply the new gate to every endpoint serving
+  real data or performing a real action, and call out anything you're
+  tempted to exclude and why. This repo shipped a token gate once that
+  covered `/api/*` but left `/frame/image` -- the actual photo bytes --
+  open; caught immediately in production.
+
+## Working in this repo
+
+- **Server tests**: `cd server && pytest` (SQLite, fixtures wipe/reseed
+  between tests -- see `tests/conftest.py`). Migration changes need a
+  matching test in `tests/test_migrations.py`; anything touching
+  `require_frame_view`/`require_frame_control` boundaries needs a
+  same-shape permission test (see `tests/test_permission_boundaries.py`
+  and `tests/test_button_actions.py` for the pattern: owner, linked user,
+  unrelated user, logged out).
+- **UI changes**: verify in a real browser (Playwright), not just by
+  reading the JS -- this project has hit multiple bugs that only showed up
+  live (mobile viewport CSS collapse, a dialog's status message landing
+  behind its own backdrop, a JSON/form-urlencoded body mismatch). Spin up
+  `uvicorn app.main:app` against a scratch `DATABASE_URL`/`CONFIG_PATH`
+  sqlite file, don't touch the real deployment's data.
+- **Deploy**: Gitea Actions at `git.thumeit.com/tfaour/espresso_frame`
+  (`.gitea/workflows/server-docker-build.yml`: `test` -> `build-and-push`
+  -> `deploy` on any push to `main` touching `server/**`; `deploy` SSHes
+  into the host as `espressoframe_deployer` and runs `docker compose pull
+  && docker compose up -d`). A separate workflow
+  (`firmware-release-build.yml`) builds+publishes firmware binaries as
+  Gitea release assets when `firmware/version.txt` changes. Poll CI status
+  with `curl https://git.thumeit.com/api/v1/repos/tfaour/espresso_frame/actions/tasks`
+  rather than asking the user to check.
+- **Device-facing paths are frozen.** `/frame/image`, `/frame/advance`,
+  `/frame/back`, `/frame/config`, `/frame/battery`, `/frame/firmware` and
+  their exact JSON key names (`refresh_interval_s`, `firmware_version`,
+  etc.) are baked into deployed firmware -- never rename or restructure
+  these without a firmware-side migration story to match.