flatpak: wire 4 store screenshots into metainfo; use GNOME 50 codecs-extra note

Screenshots pinned to a commit ref (not a branch) per Flathub guidance.
Drops the ffmpeg-full extension block (GNOME 50 uses codecs-extra); extra
codec coverage is a follow-up after the base build is confirmed.

flatpak/com.veganostr.Vega.metainfo.xml

@@ -48,17 +48,21 @@
 
   <screenshots>
     <screenshot type="default">
-      <image>https://raw.githubusercontent.com/hoornet/vega/main/flatpak/screenshots/feed.png</image>
+      <image>https://raw.githubusercontent.com/hoornet/vega/ba57143c6d46d262ec7412dcc26b85fa4a45247b/flatpak/screenshots/feed.png</image>
       <caption>The main feed with notes, reactions and zaps</caption>
     </screenshot>
     <screenshot>
-      <image>https://raw.githubusercontent.com/hoornet/vega/main/flatpak/screenshots/article.png</image>
-      <caption>Reading a long-form article</caption>
+      <image>https://raw.githubusercontent.com/hoornet/vega/ba57143c6d46d262ec7412dcc26b85fa4a45247b/flatpak/screenshots/articles.png</image>
+      <caption>Discovering long-form articles</caption>
     </screenshot>
     <screenshot>
-      <image>https://raw.githubusercontent.com/hoornet/vega/main/flatpak/screenshots/editor.png</image>
+      <image>https://raw.githubusercontent.com/hoornet/vega/ba57143c6d46d262ec7412dcc26b85fa4a45247b/flatpak/screenshots/editor.png</image>
       <caption>Writing an article in the markdown editor</caption>
     </screenshot>
+    <screenshot>
+      <image>https://raw.githubusercontent.com/hoornet/vega/ba57143c6d46d262ec7412dcc26b85fa4a45247b/flatpak/screenshots/podcasts.png</image>
+      <caption>Podcast subscriptions with value-for-value streaming</caption>
+    </screenshot>
   </screenshots>
 
   <branding>

flatpak/com.veganostr.Vega.yaml

@@ -20,14 +20,9 @@ finish-args:
   - --talk-name=org.freedesktop.secrets                # keyring crate → Secret Service (nsec storage)
   - --talk-name=org.kde.StatusNotifierWatcher          # system tray
 
-# GStreamer codecs for AAC/MP3/H.264 podcast & media playback. The base runtime
-# only ships open/royalty-free codecs.
-add-extensions:
-  org.freedesktop.Platform.ffmpeg-full:
-    directory: lib/ffmpeg
-    add-ld-path: .
-    version: "24.08"
-    autodelete: false
+# Note: extra codecs (AAC/MP3/H.264) for podcast/media playback are provided by
+# org.freedesktop.Platform.codecs-extra on the GNOME 50 runtime. Added as a
+# follow-up once the base build is confirmed.
 
 build-options:
   append-path: /usr/lib/sdk/node20/bin:/usr/lib/sdk/rust-stable/bin
@@ -79,8 +74,5 @@ modules:
       - install -Dm644 src-tauri/icons/128x128@2x.png /app/share/icons/hicolor/256x256/apps/com.veganostr.Vega.png
       - install -Dm644 src-tauri/icons/icon.png /app/share/icons/hicolor/512x512/apps/com.veganostr.Vega.png
 
-      # Create the ffmpeg extension mount point
-      - mkdir -p /app/lib/ffmpeg
-
     post-install:
       - install -Dm644 LICENSE /app/share/licenses/com.veganostr.Vega/LICENSE