refactor: clean up and refactor PR code

- Refactor duplicated video event listener boilerplate in wireVideoEvents()
  into onVideoEvent() helper (viewer.js: -57 lines)
- Fix 3 ESLint no-unused-vars warnings (bare catch instead of unused _e)
- Fix 1 additional no-unused-vars: unused 'data' param in MANIFEST_LOADED
- Remove dead 'Hls.cast' entry from playerRank map (no strategy produces it)
- Remove deprecated .eslintignore file (ESLint v9 uses flat config only)
- Add __tests__/ to ESLint ignores in flat config

Net: -20 lines (46 ins, 66 del). 83/83 tests pass, lint clean (0 warnings)

src/inject/interceptors.js

@@ -163,6 +163,6 @@
         }
       });
       observer.observe(document.head || document.documentElement, { childList: true, subtree: true });
-    } catch(_e) { /* MutationObserver not available — polling still works */ }
+    } catch { /* MutationObserver not available — polling still works */ }
   }
 })();