Doobie v0.19.0

Pitch shifter as a stand-alone effect
* Pitch Shifter is now its own card in the middle column, below
  the Delay. Works independent of delay character: pitchOn=true
  shifts the input regardless of delayMode. When delayMode IS
  Pitch and route=Feedback, the shifter is additionally injected
  into the delay's feedback character chain (classic compounding
  octave behaviour preserved).
* Dry-delay buffer aligns the dry signal with the shifter's
  algorithm latency, so dry and wet stay phase-coherent at the
  mix point — the shifter feels like a true zero-latency realtime
  effect from the listener's perspective.

Modulation matrix upgrades
* Head 1..4 Offset destinations (±50 ms via the matrix).
* Per-slot Bi / Uni polarity mode — Unipolar folds a bipolar
  source into a one-sided swell, amount sign picks direction
  (handy for sidechain ducks).
* Per-row inline source scope showing the live waveform of each
  slot's selected source.
* Amount slider now shows the live (source × amount) value as a
  bipolar fill + dot overlay.
* LFOs grow an Offset knob (bipolar DC bias on the post-depth
  output).

UI / state
* Per-head Fader gains a live VU meter on its inner edge.
* Stereo scope inside the tape loop sits properly centred between
  the strands now (uses the SVG's actual reel coordinates).
* IR browser stays open while auditioning (matches the preset
  browser flow).
* Reverb IR list / display no longer stuck on "(no IR)" after
  loading a project that has a factory IR saved — fixed a startup
  race where the emit fired before the JS listener was registered.
* User-saved presets correctly clear the dirty asterisk after save.
* Mod-drawer scrim less aggressive.
* Delay TIME knob has finer control through its useful range
  (skew centre 100 → 500 ms, drag distance doubled, step shrunk).
* Tape-character separator line removed.

Engine
* IR Speed slider drag no longer crackles (debounced reload).
* BBD clock noise AGE-scaled.
* 16 vocal-FX presets at indices 64..79 (factory bank now 80).

No breaking changes; existing presets and project files load
identically.