feat(syntonia): frequency data model and CHIRP import

[forkwright]

From Phase 02 PLAN.md, REQ-05 + REQ-06.

Frequency data model and interop:

• Typed channel struct: frequency, CTCSS/DCS tones, duplex/offset, power levels
• 50-channel family frequency plan definition
• CHIRP .img file parser: import existing radio configurations
• Convert CHIRP format to native data model
• Type safety for safety-critical radio programming (not generic maps)

Groups REQ-05 (frequency data model) and REQ-06 (CHIRP import) as the data model is the foundation for import.