Merge feat/longform-pipeline: VAD long-form pipeline, opt-in (spec 001 workstream 3)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

# Conflicts:
#	docs/Architecture.md
#	docs/Decisions.md
#	src/App.tsx
#	src/index.css
#	src/lib/engine.ts
#	src/worker/inference.worker.ts
#	src/worker/protocol.ts
#	tests/engine.test.ts
#	tests/live-real-model.test.ts
#	tests/offline.md
#	tests/protocol.test.ts

src/index.css

@@ -573,6 +573,32 @@ body {
   color: var(--muted);
 }
 
+/* --- AdvancedOptions (long-form "Skip silence", D-WS3a) --- */
+.advanced-options summary {
+  cursor: pointer;
+  color: var(--muted);
+  font-size: 0.85rem;
+}
+
+.advanced-options label {
+  display: flex;
+  align-items: center;
+  gap: 0.5rem;
+  margin-top: 0.5rem;
+  font-size: 0.9rem;
+}
+
+.advanced-options input[type="checkbox"] {
+  accent-color: var(--accent);
+}
+
+.advanced-hint {
+  margin: 0.25rem 0 0;
+  color: var(--muted);
+  font-size: 0.85rem;
+  max-width: 60ch;
+}
+
 /* --- EngineToggle (M5, D-010) --- */
 
 .engine-toggle {