Extend the RDS stack with TP/TA live updates, CT, RT+, PTYN, AF and EON support, and add UI/config controls for the new RDS feature set.

Add experimental single-sideband and vestigial-sideband stereo encoding
modes alongside the standard DSB-SC stereo subcarrier path.

- add encoder mode selection (DSB, SSB, VSB)
- add Hilbert-transform based quadrature path for SSB generation
- add vestigial split with low-band DSB and high-band SSB handling
- wire the mode through config, control, engine, generator, and fmrtx
- add test coverage for the SSB path

The default mode remains the standard DSB stereo encoder.

Embed a browser-based control surface into the HTTP server and document the live-control API. The new UI exposes TX start/stop, runtime telemetry, frequency, levels, toggles, and RDS text updates against the existing live-config endpoints.