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>

frontend/app.js

@@ -3514,7 +3514,6 @@ $('#import-btn').addEventListener('click', () => {
             }
             status.textContent = result;
             toast('Import complete!');
-            loadFeed(true);
         } catch (e) {
             status.textContent = 'Error: ' + e;
             toast('Import failed: ' + e);
@@ -3674,7 +3673,7 @@ async function init() {
             } catch (_) {}
         }
         if (isFirstRun) {
-            // First-run chooser: start fresh or import
+            // First-run: start fresh or import
             const chooser = document.createElement('div');
             chooser.className = 'image-lightbox';
             chooser.style.cursor = 'default';
@@ -3698,6 +3697,10 @@ async function init() {
                 // Open the import wizard
                 document.getElementById('import-btn')?.click();
             });
+        } else if (info && !info.hasProfile) {
+            // Not first run, but no profile set — show name setup
+            setupOverlay.classList.remove('hidden');
+            setupName.focus();
         }
         // Pre-load feed + messages from local DB (instant — no network needed)
         await loadFeed(true).catch(() => {});