fix(modular): duplicate destNames declaration in modular-ui rebuildMatrixGrid

The matrix-seeding edit from the previous commit added a second
`const destNames = engine.destNames || [];` inside rebuildMatrixGrid
while the same name was already declared earlier in the function body.
Chrome threw SyntaxError at parse time, which in turn prevented
a-app.js from wiring window.__nisps at all, which is what made the
earlier FaustWorkletProcessor error look like the root cause — it
was just the next thing that broke once the parse error let partial
modules load.

Verified end-to-end in headless Chromium via Playwright: engine
switches to modular, paramCount=32, audioCtx running, worklet node
live, zero console errors.

Also updates the Modular engine card description to reflect the new
default (32 params = 4 ADSR × 4 + 8 LFO × 2, matrix cells opt-in).

playground/js/a-app.js

@@ -1351,8 +1351,8 @@ async function init() {
     {
       id: 'modular',
       displayName: 'Modular',
-      paramCount: 512,
-      description: 'Shared mod pool (ADSRs + LFOs) routed through a matrix into a swappable voice. Starts with a 3-osc subtractive sub-engine.',
+      paramCount: 32,
+      description: 'Shared mod pool (4 ADSRs + 8 LFOs) driving a swappable voice via a routing matrix. Starts with a 3-osc subtractive sub-engine.',
     },
   ];
   const engineSwitcherEl = document.getElementById('synth-engine-switcher');

playground/js/ui/modular-ui.js

@@ -347,8 +347,7 @@ export function initModularUI({ getEngine, onStateChange } = {}) {
     // Seed current values from the engine's _lastRawByLabel map (which
     // tracks every write via setParam / _setRawByLabel / default patch),
     // falling back to the walk-entry init value for cells the user has
-    // never touched.
-    const destNames = engine.destNames || [];
+    // never touched. (destNames is already in scope from the early guard.)
     const lastRaw = engine._lastRawByLabel || new Map();
     for (let d = 0; d < destNames.length; d++) {
       const destName = destNames[d];