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/components/downloads/DownloadItem.svelte

@@ -1,5 +1,8 @@
 <script lang="ts">
   import { downloads, type DownloadInfo } from "$lib/stores/downloads";
+  import { createLogger } from "$lib/utils/logger";
+
+  const log = createLogger("DownloadItem");
 
   interface Props {
     download: DownloadInfo;
@@ -69,7 +72,7 @@
       // Refresh to update UI
       await downloads.refresh(download.userId);
     } catch (error) {
-      console.error("Failed to pause download:", error);
+      log.error("Failed to pause download:", error);
     }
   }
 
@@ -79,7 +82,7 @@
       // Refresh to update UI
       await downloads.refresh(download.userId);
     } catch (error) {
-      console.error("Failed to resume download:", error);
+      log.error("Failed to resume download:", error);
     }
   }
 
@@ -89,7 +92,7 @@
       // Refresh to update UI
       await downloads.refresh(download.userId);
     } catch (error) {
-      console.error("Failed to cancel download:", error);
+      log.error("Failed to cancel download:", error);
     }
   }
 
@@ -99,7 +102,7 @@
       // Refresh to update UI
       await downloads.refresh(download.userId);
     } catch (error) {
-      console.error("Failed to delete download:", error);
+      log.error("Failed to delete download:", error);
     }
   }
 </script>