test: add config validation and viewer integration tests

- Config validation suite (43 tests): verify HLS grid config, manifest
  dedup, video entry normalization, storage pipeline metadata preservation
- Viewer integration tests (30 tests): panel rendering for HLS/direct
  entries, edge cases (empty manifests, missing fields, mixed grids)
- Tests mirror current pipeline functions (not outdated code)

__tests__/viewer_integration.test.mjs

@@ -62,7 +62,7 @@ function createBrowserEnv({ storageData = {}, url = 'https://example.com/viewer/
   // 'native' mode sets HLS = undefined so viewer.js takes the Safari native path.
   const hlsCalls = { instances: [], loaded: false };
   if (hlsMode === 'mocked') {
-    win.HLS = class MockHLS {
+    win.Hls = class MockHLS {
       constructor(opts) {
         hlsCalls.instances.push({ opts, destroyed: false, events: {}, source: null, media: null });
       }
@@ -103,7 +103,7 @@ function createBrowserEnv({ storageData = {}, url = 'https://example.com/viewer/
   } else if (hlsMode === 'native') {
     // Simulate Safari — window.HLS exists but isSupported() returns false.
     // viewer.js then falls through to video.src = manifestUrl (native HLS).
-    win.HLS = class MockHLS_Native {
+    win.Hls = class MockHLS_Native {
       static isSupported() {
         return false; // Safari has native HLS, Hls.js is not needed
       }