Improve multicamera control and startup experience

[iffuno]

What changed

• adds persistent multicamera dashboards with independent command targets for up to four cameras
• keeps remaining cameras controllable when one disconnects and reconnects saved slots in the background
• makes REC start/stop state-aware and preserves Sony FF02 notifications as the source of truth
• simplifies the front-panel controls around target selection and REC
• restores brightness and deep sleep to a timed left-button hold
• replaces the startup sequence with a centred star-flight animation and shortens it to 0.7 seconds
• updates BLE notes, control documentation, serial diagnostics, and the README

Why

The four-camera field test exposed three practical problems: one disconnected body could disrupt the session, command targeting needed to be editable without reconnecting everything, and the startup/power controls had become less obvious than the hardware deserved.

User impact

Alphaboop can now operate any armed subset of one to four connected Sony cameras, retain disconnected slots, reconnect them automatically, and reach the dashboard faster. The camera remains responsible for confirming REC. Management declined to replace reality with optimism.

Validation

• pio run succeeds for lilygo-t-display-s3
• firmware uploaded successfully to the physical T-Display-S3 over /dev/cu.usbmodem2101
• the board responds to the serial STATUS command
• multicamera behavior was field-tested with one, two, three, and four cameras before this revision
• git diff --check origin/main...HEAD passes