Add FPV DETECT external app with Auto-scan FPV Presence Receiver (#3084)

* fpv_rx external app implemented

* FPV DETECT: PR feedback and Copilot suggestions

- Rename app from 'FPV RX' to 'FPV DETECT' (menu and title)
- Add fpv_rx to EXTAPPLIST in external.cmake so app is included in build
- Set external_apps_address_end = 0xAE010000 in external_app_info.py
- Fix clang-format in ui_fpv_rx.cpp (update_visual_state block)
- Re-sample adjacent channels during candidate verification so
  neighbor_margin lock decision uses current measurements instead of
  stale channel_memory_ from scan (reduces false/missed locks)

Made-with: Cursor

* Rename fpv_rx to fpv_detect (files, dir, app id)

- Rename directory external/fpv_rx -> external/fpv_detect
- Rename ui_fpv_rx.{cpp,hpp} -> ui_fpv_detect.{cpp,hpp}
- Update external.cmake and external.ld for fpv_detect
- Namespace fpv_rx -> fpv_detect, class FpvRxView -> FpvDetectView
- Section/symbol .app_fpv_rx -> .app_fpv_detect

Made-with: Cursor

firmware/tools/external_app_info.py

@@ -24,4 +24,4 @@
 # external app address ranges below must match those in linker file "external.ld"
 maximum_application_size = 32*1024
 external_apps_address_start = 0xADB00000
-external_apps_address_end = 0xADFC0000
+external_apps_address_end = 0xAE020000