Add LoRa FEM LNA toggle menu support

[Quency-D]

Summary

Adds an on-device screen menu for controlling the LoRa FEM LNA using the existing fem_lna_mode configuration.

This restores the screen control that was removed from #9753 without changing the protobuf definition, FEM driver, or default LNA behavior.

Changes

• Adds FEM LNA to the on-device LoRa Actions menu.
• Only shows the option when the detected FEM supports software LNA control.
  • Heltec V4.3 with KCT8103L: option is available.
  • Heltec V4.2 and earlier with GC1109: option remains hidden because its LNA cannot be bypassed through software.
  • Boards without a LoRa FEM are unaffected.
• Provides Enabled and Disabled selections and highlights the current setting.
• Applies the selected state immediately and saves it through the existing LoRa configuration flow.
• Does not require a reboot.
• Keeps the LNA enabled by default.

🤝 Attestations

• I have tested that my proposed changes behave as described.
• I have tested that my proposed changes do not cause any obvious regressions on the following devices:
  • Heltec (Lora32) V3
  • Heltec V4.2 / V4.3
  • Heltec wireless tracker V2
  • Heltec mesh node t096

Hardware testing is still required before these attestations can be checked.

Summary by CodeRabbit

• New Features
  • Added a LoRa FEM LNA menu for compatible hardware.
  • Users can enable or disable FEM LNA operation directly from the LoRa settings.
  • The menu is shown only when supported hardware controls are available.
  • Changes are applied immediately and reflected in the device configuration.

[github-actions]

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: f9d52c44-dcd5-4055-b347-ae3562f3543c

📥 Commits

Reviewing files that changed from the base of the PR and between 41c5c92 and 47f80cc.

📒 Files selected for processing (2)

• src/graphics/draw/MenuHandler.cpp
• src/graphics/draw/MenuHandler.h

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📝 Walkthrough

Walkthrough

Changes

LoRa FEM LNA menu

Layer / File(s)	Summary
Menu contract and FEM entry src/graphics/draw/MenuHandler.h, src/graphics/draw/MenuHandler.cpp	When HAS_LORA_FEM is enabled and controllable hardware is available, the LoRa menu adds the FEM LNA option and routes selection to the new menu.
FEM LNA toggle handling src/graphics/draw/MenuHandler.cpp	The new menu supports Back, Enabled, and Disabled. Valid changes update the FEM LNA configuration, apply the hardware state, reload configuration, and log the result.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Suggested reviewers: nomdetom

Sequence Diagram(s)

sequenceDiagram
  participant User
  participant menuHandler
  participant LoRaFEMInterface
  participant DeviceConfiguration
  participant Logger
  User->>menuHandler: Select FEM LNA mode
  menuHandler->>LoRaFEMInterface: Update and apply LNA state
  menuHandler->>DeviceConfiguration: Reload configuration
  menuHandler->>Logger: Log FEM LNA state

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🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: adding a LoRa FEM LNA toggle menu.
Description check	✅ Passed	The description explains the purpose, behavior, hardware conditions, and implementation scope, but it contains a minor testing-attestation contradiction.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

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[iv3dxw]

Hello
I don't think this feature will be useful.
I tested (FW 2.7.20) Heltec wireless tracker V2 and RX is good: no overload causing sensitivity degradation, correct RSSI reports, correct noise floor value. From my point of view no need to control LNA enable/disable from user interface.
I'm not sure that Heltec V4.3 has the same behaviour of Heltec wireless tracker V2.

The main problem is the Heltec V4.2 is still not working well even with 2.7.26:
I have overload causing sensitivity degradation, RSSI is about 15dB higher and also noise floor is higher.
I can use my Heltec V4.2 only inserting band pass filter at antenna input.
Also in this case the user define LNA mode is not needed: Heltec V4.2 needs to have external LNA gain compensated in internal AGC, nothing else from my point of view.

Thanks