feat(syntonia): BF-F8HP + UV-5RM Plus variant support

[forkwright]

Summary

• RadioVariant enum with per-variant config (magic bytes, power mapping, aux flags)
• Firmware prefix matching for variant identification (UV-5R, BF-F8HP, UV-5RM Plus)
• Tri-power support for BF-F8HP (8W/4W/1W) and UV-5RM Plus (assumed 10W/5W/1W)
• Variant-aware codec and protocol (aux warm-up, dropped-byte workaround at 0x1FCF)
• Auto-detect flow trying multiple magic byte sets with graceful failure message
• UV-5RM Plus: suggests UV17Pro protocol investigation if UV-5R family detection fails

Test plan

• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test --workspace — 84 tests pass (47 baofeng-specific)
• Variant identification from known firmware prefixes (BFB→UV-5R, BFP3V3→F8HP)
• Power level round-trip per variant (2-level UV-5R, 3-level F8HP)
• UV-5R Mid bits treated as High (cross-radio import safety)
• Auto-detect with mock serial (success + failure paths)
• F8HP download plan includes aux warm-up and dropped-byte split
• UV-5R download plan skips aux region

🤖 Generated with Claude Code

[github-actions]

⚠️ Large PR detected — 15 files, 2592 lines changed.

Consider splitting into smaller PRs for easier review. Not a blocker, just a signal.