feat(settings): add 2.8 amateur and EU Lite/Narrow LoRa regions

[jamesarich]

Adds the 2.8 firmware regions to the region picker: ITU1/2/3 2m, ITU2 1.25m, ITU1/2/3 70cm, plus EU_866 (Lite) and EU_N_868 (Narrow).

• RegionInfo.minFirmware + Capabilities.supportsRegion() hide them from pre-2.8 targets, remote admin included; the current selection is never hidden
• slot math now mirrors firmware applyModemConfig: per-profile spacing/padding and fixed default slots, so e.g. ITU2_70CM shows slot 137 @ 433.650 MHz
• preset gating generalized the same way: ChannelOption.minFirmware + supportsPreset() replace the hardcoded TINY filter, and now also gate MEDIUM_TURBO and LITE/NARROW — all 2.8-only in firmware (LITE/NARROW enum values shipped in v2.7.23 protobufs, but the modemPresetToParams cases are 2.8; older firmware silently falls back to LongFast)
• tests pin slot counts, default frequencies, and the gated region/preset sets to the firmware table

Fixes #6547

[coderabbitai]

📝 Walkthrough

Walkthrough

The model adds EU and ITU radio regions with regional slot parameters and firmware requirements. Frequency calculations honor spacing, padding, and fixed slots. Capabilities filter unsupported regions from the settings dropdown while preserving the current selection. Tests cover mappings, calculations, and firmware gating.

Changes

Regional radio support

Layer / File(s)	Summary
Regional metadata and frequency calculations core/model/src/commonMain/kotlin/org/meshtastic/core/model/ChannelOption.kt	RegionInfo now stores spacing, padding, fixed-slot, and minimum-firmware metadata. Channel calculations use regional slot widths. EU and ITU regions are added.
Firmware capability filtering in settings core/model/src/commonMain/kotlin/org/meshtastic/core/model/Capabilities.kt, feature/settings/src/commonMain/kotlin/org/meshtastic/feature/settings/radio/component/LoRaConfigItemList.kt	Capabilities.supportsRegion checks firmware requirements. The region dropdown filters unsupported regions and retains the selected region.
Regional behavior validation core/model/src/commonTest/kotlin/org/meshtastic/core/model/CapabilitiesTest.kt, core/model/src/commonTest/kotlin/org/meshtastic/core/model/RegionInfoTest.kt	Tests cover firmware gating, region mappings, EU and ITU frequencies, legacy US calculations, and explicit channel selection.

Estimated code review effort: 4 (Complex) | ~45 minutes

Sequence Diagram(s)

sequenceDiagram
  participant LoRaConfigItemList
  participant Capabilities
  participant RegionInfo
  LoRaConfigItemList->>Capabilities: check supportsRegion(region)
  Capabilities->>RegionInfo: read minFirmware
  RegionInfo-->>Capabilities: return firmware requirement
  Capabilities-->>LoRaConfigItemList: return supported status
  LoRaConfigItemList-->>LoRaConfigItemList: build filtered region dropdown

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🚥 Pre-merge checks | ✅ 3 | ❌ 3

❌ Failed checks (3 warnings)

Check name	Status	Explanation	Resolution
Linked Issues check	⚠️ Warning	The PR adds all listed amateur regions, but no evidence shows support for the required TinyFast and TinySlow presets.	Implement and expose TinyFast and TinySlow presets with the required capability gating.
Out of Scope Changes check	⚠️ Warning	The EU_866 and EU_N_868 regions are not included in linked issue #6547, which specifies amateur regions and TinyFast/TinySlow presets.	Remove the EU region changes or link an issue that explicitly requires them.
Tests Prove The Path, Not The End State	⚠️ Warning	Two added tests are non-discriminating: standard_regions_keep_legacy_slot_math matches parent behavior, and explicit_channel_num_wins_over_override_slot exercises the pre-existing explicit-chan...	Replace or strengthen these tests. Assert a new region's fixed default slot without channel_num, and verify spacing/padding changes the slot count and frequency.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Sibling Call Sites And Presence Semantics	✅ Passed	The new nullable minFirmware is handled by supportsRegion and has no other call sites; spacing/padding/overrideSlot zero defaults are documented sentinels, not sensor fields. No unfixed NodeItem si...
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely identifies the added firmware 2.8 amateur and EU Lite/Narrow LoRa regions.

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In
`@core/model/src/commonTest/kotlin/org/meshtastic/core/model/RegionInfoTest.kt`:
- Around line 101-122: Add explicit numChannels assertions for both ITU3_2M and
ITU3_70CM in ham_70cm_and_125cm_regions_use_100kHz_slots, expecting 200 slots
for each region. Keep the existing frequency and channel-selection assertions
unchanged.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: 98e71c3e-86e9-4bc5-b0b7-8f3f92eec584

📥 Commits

Reviewing files that changed from the base of the PR and between 7bee4ff and d6870fa.

📒 Files selected for processing (5)

• core/model/src/commonMain/kotlin/org/meshtastic/core/model/Capabilities.kt
• core/model/src/commonMain/kotlin/org/meshtastic/core/model/ChannelOption.kt
• core/model/src/commonTest/kotlin/org/meshtastic/core/model/CapabilitiesTest.kt
• core/model/src/commonTest/kotlin/org/meshtastic/core/model/RegionInfoTest.kt
• feature/settings/src/commonMain/kotlin/org/meshtastic/feature/settings/radio/component/LoRaConfigItemList.kt