docs: track remaining flight-controller work

List the remaining physical flight integration, peripheral support and
hardware verification tasks.

.todo

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+- Run the flight runtime from RTIC with physical sensor input.
+- Persist vehicle settings and sensor calibration in board configuration.
+- Carry IMU acquisition times, uncertainty and complete sample batches into navigation.
+- Add range and optical-flow fusion for local navigation.
+- Add hardware motor-output drivers using the existing DShot and PWM code.
+- Connect motor outputs to arming, failsafe and command-expiry handling.
+- Add private MAVLink commands for arming, disarming and onboard missions.
+- Inhibit motors during configuration flash writes.
+- Add onboard barometer drivers and shared I2C bus access.
+- Add battery-voltage, current and analog RSSI acquisition.
+- Add onboard flash storage and blackbox recording.
+- Add analog OSD support.
+- Add buzzer, LED-strip, camera-control and auxiliary-output drivers.
+- Add receiver, GPS, VTX and ESC telemetry support to configurable ports.
+- Complete board component identification and peripheral pin maps.
+- Add hardware tests for sensor decoding, calibration, timing and recovery.
+- Add hardware tests for motor shutdown on reset, missed deadlines and faults.
+- Measure startup time, control-loop latency and peak stack under I/O load.
+- Verify onboard takeoff, hover, landing and motor shutdown on hardware.