Add IN_433 regulatory region code

[kholia]

What does this PR do?

Append IN_433 as RegionCode 38 without renumbering existing values. This prepares generated bindings and firmware support for India's 433.05-434.79 MHz allocation under G.S.R. 347(E), 2022.

Regulatory source: https://eservices.dot.gov.in/sites/default/files/circular-notifications/the-use-of-low-power-radio-frequency-devices-in-the-frequency-band-433.05-to-434.79-mhz-exemption-from-license-rules-2022.pdf

Current DoT spectrum-plan context: https://www.dot.gov.in/static/uploads/2026/02/52e468605d5b63c6dfedcf538f1d7d36.pdf

PDF attached here for easy reference.

[UPDATED] Related firmware context: meshtastic/firmware#11268

On why we need a different region configuration:

   Existing region    Why it cannot represent India safely
  ━━━━━━━━━━━━━━━━━  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
   ANZ_433            Same frequency range, but permits 14 dBm and 100% duty cycle.
  ─────────────────  ───────────────────────────────────────────────────────────────────────────────
   UA_433             Same 10 dBm/10%, but starts at 433.00 MHz—below India’s 433.05 MHz boundary.
  ─────────────────  ───────────────────────────────────────────────────────────────────────────────
   EU_433             Also starts below the Indian boundary and stops at 434.00 MHz.
  ─────────────────  ───────────────────────────────────────────────────────────────────────────────
   KZ_433             Frequency is a legal subset and power is 10 dBm, but permits 100% duty cycle.

Checklist before merging

• All top level messages commented
• All enum members have unique descriptions

Summary by CodeRabbit

• New Features
  • Added support for the India 433 MHz regional configuration.
  • Included documentation for the new regional option.

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[coderabbitai]

📝 Walkthrough

Walkthrough

Adds the documented IN_433 = 38 value to LoRaConfig.RegionCode in meshtastic/config.proto.

Changes

LoRa region code update

Layer / File(s)	Summary
Add India 433MHz region code meshtastic/config.proto	LoRaConfig.RegionCode now includes the documented IN_433 = 38 enum value.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Possibly related PRs

• meshtastic/protobufs#985: Modifies the same LoRaConfig.RegionCode enum and uses numeric code 38.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
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.
Title check	✅ Passed	The title clearly summarizes the main change by adding the IN_433 region code.
Description check	✅ Passed	The description matches the template’s main sections and includes the required checklist items, with the change and rationale clearly explained.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[kholia]

Hey Folks - How do we move this PR forward? Thank you!

[kholia]

The corresponding firmware PR is @ meshtastic/firmware#11268 URL now.

[caveman99]

This will be covered by EU_433 from version 3.0 - see meshtastic/firmware#2696 - up to that point you need to use EU_433