lotus(#1): gate in-source denoise on dedicated lotusDenoiseSource flag

The host already sets lotusDenoise=ml and injects its getUserMedia shim;
reusing that flag would double-process audio the moment this fork ships.
Gate the in-source engine on lotusDenoiseSource=1 instead, so the fork is
inert on deploy and the host cuts over explicitly (set the flag + drop the
shim) when ready.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/lotus/lotusDenoise.ts

@@ -56,7 +56,13 @@ function safeAssetBase(raw: string | null): string {
 }
 
 export function startLotusDenoise(vm: CallViewModel): () => void {
-  if (lotusParam("lotusDenoise") !== "ml") return () => undefined;
+  // Gate on a DEDICATED flag — NOT the existing `lotusDenoise=ml` that the
+  // host's build-time getUserMedia shim already uses. Otherwise simply shipping
+  // this fork (while the host still injects its shim and still sets
+  // lotusDenoise=ml) would denoise twice. The host opts into the in-source
+  // engine with `lotusDenoiseSource=1` AND stops injecting the shim at the same
+  // time. Default off ⇒ the fork is inert and behaviour is unchanged.
+  if (!lotusFlag("lotusDenoiseSource")) return () => undefined;
 
   const requested = lotusParam("lotusModel");
   const model: LotusDenoiseConfig["model"] =