Improve attachment memory safety, downloads, and high-memory alert UX.

Stream large receives to disk with chunk acks to cap renderer RAM, evict
off-screen display blobs, and route exports through a disk-aware download
service. Fix the high-memory dialog (backdrop dismiss, copy, log actions),
allow diagnostics paths in the path jail, and restore persisted image
hydration after reload.

Co-authored-by: Cursor <cursoragent@cursor.com>

toju-app/public/i18n/catalog/settings.json

@@ -441,7 +441,9 @@
       "title": "App-wide debugging",
       "description": "Capture UI events, navigation activity, console output, and global runtime errors in a live debug console.",
       "processRam": "Process RAM",
-      "ramHint": "Live total working set from Electron app metrics. Updates every 2 seconds.",
+      "exportRamDiagnostics": "Export RAM diagnostics",
+      "exportRamDiagnosticsWorking": "Exporting...",
+      "ramHint": "Live total working set from Electron app metrics. Updates every 2 seconds. Export saves a diagnostics log and opens the high-memory alert dialog.",
       "capturedEvents": "Captured events",
       "lastUpdate": "Last update: {{label}}",
       "noLogsYet": "No logs yet",