Add experimental Xteink X3 camera remote support

[LittleBidet]

Summary

Add experimental Xteink X3 support as dedicated ESP32-C3 camera-remote firmware, replacing the ebook reader application. The portrait e-ink interface provides front-button navigation, a dedicated right-side shutter button, camera discovery, saved connections, focus, bulb lock, and an intervalometer.

Includes X3 build/release and web-installer support, UC8253/UC8279d display drivers, battery reporting and power-button deep sleep, and PlatformIO installation instructions. X3 supports up to two camera connections; reader functions, SD storage, GPS and OTA are not exposed. Automatic light sleep and dynamic frequency scaling are not enabled.

Shared control changes and M5 behavior

E-ink refreshes can outlast a button press. X3 polls input and advances interval timing separately from rendering, with another worker handling scanning and connections. The shared layer owns camera lifetimes and command queues, so synchronization and cancellation handling also affect existing M5 targets.

The M5 behavior changes are:

• An empty target set now leads to STATE_CONNECT_FAILED. Previously, an empty vector satisfied allConnected() and could open an empty connected menu.
• The reconnect failure count is a member reset by each explicit connectAll(bool) call. The previous function-static count leaked across sessions.
• Connection generations discard stale queued commands after cancellation or reconnect. Presses submitted outside STATE_ACTIVE are rejected instead of queued; accepted release requests are preserved through reconnect.
• UI::doConnect() returns early outside STATE_IDLE. Failure to add a target or start a connection calls doDisconnect() to clean up partial setup.
• updateGPS() uses a nonblocking mutex attempt and drops that update when connection work holds the mutex, keeping the UI responsive.
• Each web-installer manifest now declares one matching chipFamily. Previously, each M5 manifest offered both ESP32 and ESP32-S3 entries using the same board binaries. ESP Web Tools can now refuse an incompatible chip selection.

Queue overflow rejects the affected press without permanently disabling future presses. Releases that cannot be queued are recorded for retry and report acceptance consistently. Dropping one camera does not automatically release every target; explicit releases can reach still-connected cameras during reconnect without waiting for the connection mutex. Target writes check connectivity, and cumulative failure counters keep X3 command errors observable across overwritten status snapshots.

X3 startup failures use a board-neutral fatal hook with best-effort deep sleep instead of repeated rebooting; the default M5 handler remains abort(). The follow-up also separates the display-independent interval timer name from the M5 UI class, removes renderer title-string detection and dead lifecycle cases, and corrects font licensing/source metadata.

Validation

• Initial hardware bring-up was tested on an Xteink X3 with a UC8253 panel and Fujifilm X-T4. All three firmware images were verified by readback; startup logs showed successful panel detection without display errors or a reboot loop.
• The initial port was built for all six environments. The latest follow-up changes were rebuilt for Xteink X3 and M5Stick-C.
• Local control, interval timing, X3 app and renderer checks passed, including accepted releases during a stalled reconnect and persistent error reporting through overwritten snapshots. Formatting and diff checks passed. The validation harness remains local and is not included in this contribution.

The latest follow-up still needs hardware regression testing. UC8279d panel behavior, multi-camera behavior, battery accuracy and sleep/wake behavior need hardware validation. Testing one camera/device combination does not establish compatibility with every supported camera.

Assisted-by: OpenAI Codex