AppImage video fix, proper import posts, first-run chooser, file pickers

- bundleMediaFramework: true — bundles full GStreamer plugin set in AppImage.
  Fixes WebKit hang on video/audio (missing appsink/autoaudiosink plugins).
  MSDK/VA plugins removed post-build to avoid Ubuntu DMA assertion crash.
- Import creates complete posts: BlobHeader, VisibilityIntent, pinned blobs,
  self-follow. Imported posts now indistinguishable from locally created ones.
- First-run chooser: Start Fresh or Import Identity on fresh install only.
  Profile setup shown for existing identities without display name.
- File pickers: native Browse buttons on export (folder) and import (ZIP)
  via tauri-plugin-dialog.
- Export path: relative paths resolved against home dir.
- Lightbox close: only on overlay/image click, not inner form content.
- Growth loop skips self as N2 candidate.
- Node shutdown on identity switch (prevents zombie background tasks).
- media-src CSP includes asset protocol.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/tauri-app/tauri.conf.json

@@ -18,7 +18,7 @@
       }
     ],
     "security": {
-      "csp": "default-src 'self'; script-src 'self' 'unsafe-inline'; style-src 'self' 'unsafe-inline'; img-src 'self' blob: http://asset.localhost; media-src 'self' blob:",
+      "csp": "default-src 'self'; script-src 'self' 'unsafe-inline'; style-src 'self' 'unsafe-inline'; img-src 'self' blob: http://asset.localhost; media-src 'self' blob: http://asset.localhost",
       "assetProtocol": {
         "enable": true,
         "scope": ["$APPDATA/**", "$HOME/.local/share/itsgoin/**"]
@@ -33,6 +33,11 @@
       "icons/128x128@2x.png",
       "icons/icon.icns",
       "icons/icon.ico"
-    ]
+    ],
+    "linux": {
+      "appimage": {
+        "bundleMediaFramework": true
+      }
+    }
   }
 }