feat: Add three interactive synthesizers to Web Audio Playground

- Bass Synthesizer (C2-C3)
  * Deep bass tones with portamento (pitch glide)
  * Sawtooth/square waveform selector
  * 50ms portamento, 300ms release envelope

- Lead Synthesizer (C5-C6)
  * High octave leads with LFO vibrato
  * Interactive controls: vibrato rate (3-10Hz), depth (5-20Hz)
  * Lowpass filter with cutoff control (500-5000Hz)
  * Bright sawtooth waves

- Chord Pad Synthesizer
  * 8 chord presets (C Major, C Minor, F, G, Am, Dm, Em, G7)
  * Multiple detuned oscillators (±8 cents) for rich textures
  * Interactive attack (0.1-1.0s) and release (0.3-2.0s) controls
  * Slow ADSR for ambient pads

Technical improvements:
- Extended note-frequencies map to C2-C6 (38 notes total)
- Created reusable slider-control and waveform-selector components
- Added 6 Reagent atoms for real-time parameter control
- All synthesizers properly wired with interactive controls

Files modified:
- src/scittle/audio/audio_playground.cljs: +~300 lines
- Added 3 synthesizer functions, 3 UI components, 6 interactive controls

Author: burinc