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/app.json

@@ -18,8 +18,10 @@
     },
     "highMemoryAlert": {
       "badge": "High memory usage",
-      "title": "The app used {{usageGb}} GB of RAM last session",
-      "message": "A diagnostics log was saved in your app data folder. You can open it now or copy the path if you want to share it with support.",
+      "thresholdTitle": "The app is using {{usageGb}} GB of RAM",
+      "thresholdMessage": "MetoYou crossed the 2 GB memory threshold. A diagnostics log was saved so you can inspect what was using memory or share it with support.",
+      "manualTitle": "RAM diagnostics exported ({{usageGb}} GB in use)",
+      "manualMessage": "A snapshot of current memory usage was saved. Open the log, reveal it in your file manager, or copy the path to share with support.",
       "openLog": "Open log file",
       "showInFolder": "Show in folder",
       "copyPath": "Copy path",