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/core/src/network.rs

@@ -1561,6 +1561,10 @@ impl Network {
                 };
 
                 let (candidate_id, score) = match candidate {
+                    Some((nid, score)) if nid == self.our_node_id => {
+                        debug!("Growth loop: skipping self as candidate");
+                        continue;
+                    }
                     Some(c) => c,
                     None => {
                         debug!("Growth loop: no N2 candidates available");