feat(web): merge Song Importer into Global Suche (one unified field)

The importer no longer has its own sidebar/bottom-nav entry. The Global
Suche field now handles both jobs: plain text runs the Deezer search;
a pasted Spotify/SoundCloud/YouTube link switches into importer mode
(badge + "Importieren" button + preview), matching the Android app and
tidying the left nav.

- New onGlobalInput/tryImporterResolve; importer DOM moved into
  page-discover; old page-spotify-importer removed; routing cleaned up.
- Existing resolvers unchanged (still read the mirrored importer-link-input).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/main.js

@@ -24,7 +24,7 @@ import {
   plReorderEnter, plReorderSave, plReorderCancel, toggleAllGenres,
 } from './views/views.js';
 import { loadSpotifyImporter, resolveSpotifyLink, clearSpotifyPreview, spotifyDlAll,
-         onImporterInput, resolveImporterLink } from './views/spotify.js';
+         onImporterInput, resolveImporterLink, onGlobalInput, tryImporterResolve } from './views/spotify.js';
 import { resolveYouTubeLink, executeYouTubeDownload } from './views/youtube.js';
 import { loadSoundCloudImporter, resolveSoundCloudLink, clearSoundCloudPreview, scDlAll, scDlSingle, scDlTrack } from './views/soundcloud.js';
 import {
@@ -343,7 +343,7 @@ Object.assign(window, {
   loadAlbums, loadStarred, loadRandom, filterStarred, filterPlaylist,
   plReorderEnter, plReorderSave, plReorderCancel, toggleAllGenres,
   loadSpotifyImporter, resolveSpotifyLink, clearSpotifyPreview, spotifyDlAll,
-  onImporterInput, resolveImporterLink,
+  onImporterInput, resolveImporterLink, onGlobalInput, tryImporterResolve,
   loadSoundCloudImporter, resolveSoundCloudLink, clearSoundCloudPreview, scDlAll, scDlSingle, scDlTrack,
   executeSpotifyDownload, resolveYouTubeLink, executeYouTubeDownload,
   openPlModal, closePlModal, addSongsToPlaylist, createAndAddPlaylist, createPlaylistPrompt,