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/routes/downloads/+page.svelte

@@ -21,6 +21,9 @@
   import { auth } from "$lib/stores/auth";
   import DownloadItem from "$lib/components/downloads/DownloadItem.svelte";
   import DownloadedBrowse from "$lib/components/downloads/DownloadedBrowse.svelte";
+  import { createLogger } from "$lib/utils/logger";
+
+  const log = createLogger("DownloadsPage");
 
   type ViewType = "downloaded" | "transfers";
   let view = $state<ViewType>("downloaded");
@@ -42,7 +45,7 @@
         await downloads.refresh(userId);
       }
     } catch (error) {
-      console.error("Failed to load downloads:", error);
+      log.error("Failed to load downloads:", error);
     } finally {
       loading = false;
     }
@@ -60,7 +63,7 @@
         try {
           await downloads.pause(download.id);
         } catch (error) {
-          console.error(`Failed to pause download ${download.id}:`, error);
+          log.error(`Failed to pause download ${download.id}:`, error);
         }
       }
     }
@@ -74,7 +77,7 @@
         try {
           await downloads.resume(download.id);
         } catch (error) {
-          console.error(`Failed to resume download ${download.id}:`, error);
+          log.error(`Failed to resume download ${download.id}:`, error);
         }
       }
     }