Fix Photos save for images + add native Quick Look file preview

Photos/Files bug: the lightbox download handed nativeSaveFile a bare
"/files/<id>" with no name, extension, or mime. Empty mime made
bzSaveToPhotos short-circuit as "notmedia" — so saveToAlbum (and its
permission prompt) never ran, and the image landed in the generic Files
folder as an extension-less blob. Now nativeSaveFile trusts the server's
Content-Type when the mime is unknown and appends a real extension
(bzExtForMime/bzEnsureExt), so images reach the Images folder AND Photos.

File preview: replace the @capacitor/share "share sheet" open with a new
native FileOpener plugin (QLPreviewController). bzOpenFile now prefers a
real Quick Look preview and only falls back to the share sheet if the
plugin isn't in the build. Wired file-opener into mobile/package.json and
the codemagic SPM diagnostics loop.

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

codemagic.yaml

@@ -54,7 +54,7 @@ workflows:
           echo "iOS project layout:"; ls -la ios/App
           # ── Diagnose local-plugin SPM wiring (the regression: our file: plugins didn't function at runtime) ──
           echo "=== local plugins in node_modules — symlink vs copy, and is Package.swift present? ==="
-          for p in native-call media-library audio-route share-inbox; do
+          for p in native-call media-library audio-route share-inbox file-opener; do
             echo "-- $p --"; ls -ld "node_modules/$p" 2>/dev/null || echo "  (dir missing)"
             ( ls "node_modules/$p/Package.swift" >/dev/null 2>&1 && echo "  Package.swift PRESENT" ) || echo "  Package.swift MISSING"
           done