Felt Orbit v191 - KEYSTARS + FRAME BUDGET + VIBRATO ZERO-RATE FIX

Fix:
- When samp_vib_rate is 0, the vibrato LFO contribution is forced to 0.
- This prevents Vibrato Depth from becoming a static pitch offset when the LFO is stopped at a non-zero phase.
- For vibrato rate > 0, the original vibrato path/character is preserved.
- OLED key-stars, frame-budget fix, and raw host knob handling are unchanged.
