fix: lazy-resolve image dimensions for providers without width/height metadata (Pawchive)

- Convert _PostInfoCard to StatefulWidget
- Lazily decode real pixel dimensions (e.g. 1920×1080) from network when post.width==0 && post.height==0
- Show '… × …' while resolving, actual size once decoded
- Hide resolution badge for video/link posts where dimensions can't be resolved
- In-memory cache prevents redundant re-downloads
- Bump version to 2.3.7+47

lib/app/changelog.dart

@@ -1,4 +1,13 @@
 const lunarisChangelog = [
+  LunarisChange(
+    version: '2.3.7',
+    title: 'Lazy Media Dimensions for Pawchive & Unknown-Size Providers',
+    bullets: [
+      'Auto-Resolve Image Dimensions: when a provider (such as Pawchive) does not supply width/height metadata, the app now lazily resolves the real pixel dimensions by decoding the image in the background and displays them as soon as they are ready.',
+      'No More "0 × 0": the resolution badge now shows "… × …" while dimensions are being fetched, and the correct resolution (e.g. 1920 × 1080) once decoded. The badge is hidden entirely for video/link posts where dimensions cannot be resolved.',
+      'Session Cache: resolved image dimensions are cached in memory for the lifetime of the app so repeated visits to the same post do not trigger re-downloads.',
+    ],
+  ),
   LunarisChange(
     version: '2.3.6',
     title: 'Pawchive Accounts Integration & Favorites Synchronization',