v0.4.2: Welcome screen, status ticker, notifications, text scaling, networking fixes

Welcome screen with staggered counters while backend bootstraps. Header status
ticker for new posts/messages/reactions/comments/connection changes. Notification
fallback chain (Tauri plugin → Web API → notify-rust). Responsive text scaling
(Small/Normal/Large, persisted). Diagnostics moved to popover with on-demand
connections. Share details lightbox with QR code. Connect string prefers external
address. Stale N1 fix (disconnected routes excluded). Replication handler actively
fetches posts+blobs from requester. Hole punch registers remote address for relay.
Replication semaphore (3 concurrent). Peer labels show truncated node ID.

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

crates/tauri-app/tauri.conf.json

@@ -1,6 +1,6 @@
 {
   "productName": "itsgoin",
-  "version": "0.4.1",
+  "version": "0.4.2",
   "identifier": "com.itsgoin.app",
   "build": {
     "frontendDist": "../../frontend",