docs: Pi install + pm3flash firmware flashing (README, CLAUDE, roadmap)

- README: rewrite Install (from source, submodules, deps, Pi/aarch64); new
  'Flashing firmware (pm3flash)' section — CLI usage, --build, image resolution,
  cross-compile + PLATFORM note, Raspberry Pi bring-up, programmatic API; point
  Firmware Compatibility at it; add a License section (MIT).
- CLAUDE.md: flash.py/_firmware.py/flash_cli.py in the structure; a 'Firmware
  flashing' section with the maintainer gotchas (OLD frame, fullimage-only,
  page-merge, platform != is_rdv4, the pin).
- roadmap: new 2026-07-05-firmware-flasher plan doc + a Firmware-flashing row.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/plans/README.md

@@ -49,6 +49,12 @@ approach, concrete steps, tests, risks.
 | [2026-07-03-firmware-upstream-rebase-plan](2026-07-03-firmware-upstream-rebase-plan.md) | 📎 | Rebase the `proxmark3-pm3py` fork against upstream PM3 (atomic single-file-commit workflow). |
 | [2026-07-05-firmware-fork-dt-migration](2026-07-05-firmware-fork-dt-migration.md) | 📋 | Migrate the firmware fork + pm3py to the DT Gitea; clean `master`(RRG-mirror)/`pm3py`(patches) rebase-fork model. |
 
+## Firmware flashing
+
+| Plan | Status | Summary |
+|------|--------|---------|
+| [2026-07-05-firmware-flasher](2026-07-05-firmware-flasher.md) | ✅ | Pure-Python flasher (OLD-frame bootloader protocol) + `pm3flash` CLI + firmware pin; hardware-validated on a PM3 Easy. Auto-download of the pinned release is the open follow-up (rides on the DT-Gitea migration). |
+
 ---
 
 ### Conventions