refactor(logging): route frontend console calls through the logger

TRACES: | DR-204

484 ungated `console.*` calls across 63 non-test frontend files shipped to
end users with no way to turn them off. Mechanical substitution, no control
flow, error handling or message semantics changed:

  console.log / console.debug -> log.debug
  console.info                -> log.info
  console.warn                -> log.warn
  console.error               -> log.error

Hand-written `"[Scope] …"` prefixes are dropped where the logger's scope
now carries them; scope names that already existed are preserved verbatim
(`[Auth]`, `[VideoPlayer]`, `[PiP]`, …) and inferred from the filename
where a file had none. `src/routes/player/[id]/+page.svelte` keeps its
`NextEpisode` and `AutoPlay` sub-scopes as separate loggers rather than
flattening them into the page scope.

`grep -rn 'console\.' src/` now matches nothing outside the tests and the
facade itself.

src/lib/utils/backgroundAudio.ts

@@ -18,6 +18,10 @@
  * Unsupported (no-op) on every non-Android platform.
  */
 
+import { createLogger } from "$lib/utils/logger";
+
+const log = createLogger("BgAudio");
+
 interface AndroidBackgroundAudioBridge {
   setEnabled(enabled: boolean): void;
 }
@@ -44,15 +48,15 @@ export function setBackgroundAudioEnabled(enabled: boolean): boolean {
     // before/without the bridge existing. Silently no-oping here leaves the UI
     // showing "armed" while native never learns — and the handoff then never
     // fires on lock. Report it so callers can retry.
-    console.warn("[BgAudio] setEnabled: bridge missing, native NOT armed");
+    log.warn("setEnabled: bridge missing, native NOT armed");
     return false;
   }
   try {
     b.setEnabled(enabled);
-    console.log("[BgAudio] setEnabled ->", enabled);
+    log.debug("setEnabled ->", enabled);
     return true;
   } catch (err) {
-    console.warn("[BgAudio] Failed to set enabled:", err);
+    log.warn("Failed to set enabled:", err);
     return false;
   }
 }