docs: add firmware developer guide (build/flash/debug)

New tutorial "Building, flashing, and debugging the firmware" covering the
full firmware-developer loop, verified against the openmv firmware, OpenMV
IDE, and OpenMV SDK sources:

- VS Code + extensions, WSL install, the SDK-driven toolchain (make sdk),
  cloning/submodules, and the per-board build (mpy-cross + make TARGET)
  with a complete board table and build-artifact list.
- Build options table (DEBUG/V/DEBUG_PRINTF/PROFILE_ENABLE/...).
- On-hardware debugging: DEBUG=1, J-Link/SWD, per-MCU J-Link device
  table, Cortex-Debug launch.json, SVD, the Windows<->WSL J-Link bridge
  (jlink/external + usbipd-win), make debug, gdb usage, OpenOCD, pitfalls.
- Flashing split into two sections with per-family detail: OpenMV IDE
  Load Custom Firmware, Windows USB drivers, make deploy (SWD), STM32
  dfu-util (App/DFU VID:PID table), AE3 dual-core alt-map table, RT1062
  NXP SPSDK, Arduino (dfu-util + bossac + picotool), per-board
  filesystem-erase table.
- Restoring the bootloader: STM32 BOOT-RST jumper, N6 CubeProgrammer,
  RT1062 SDP/SBL recovery, AE3 Alif SE Tools (tooling + MRAM tables),
  Arduino factory-locked note.

Added to the tutorial toctree after tls_certificates.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: kwagyeman