Add smooth interpolation, encoder acceleration, and persistence

[joaodotwork]

Description

Polish the control surface UX with smooth display animations, velocity-sensitive encoder acceleration, FX grouping, and persistent mappings.

Tasks

• Smooth arc interpolation — animate value changes over 2–3 frames
• Encoder acceleration — larger increments for faster rotation
• Parameter grouping by FX chain (auto-organize discovered parameters)
• Persist encoder-to-parameter mapping to JSON config file
• Restore mapping on bridge restart
• Add configurable color themes for parameter arcs (per-group or per-type)
• Encoder sensitivity CLI option (--sensitivity)

Acceptance Criteria

• Arc indicators animate smoothly, not jumping between values
• Fast encoder turns move parameters more than slow turns
• Parameters are logically grouped (e.g., all blur params together)
• Mappings survive bridge restart
• Visual polish feels comparable to Ableton's native display

Technical Notes

• Encoder sends 1–63 for CW, values increase with rotation speed
• Acceleration curve: delta * (1 + abs(raw_delta) * accel_factor)
• ~210 steps per full rotation at base speed
• Persistence: save to ~/.push2-bridge/mappings.json or project-local config