Fix desktop crate build; simplify tray/menu and telemetry reconnect

Real bugs found by actually compiling the Tauri crate for the first time:
- Cargo.toml declared a [lib] with no src/lib.rs (cargo refused to parse
  the manifest) — added the standard Tauri 2 main.rs/lib.rs split.
- generate_context!() needs real icon files; icons/ only had a .gitkeep.
  Added placeholder PNG/ICO/ICNS icons.

Also simplified: dropped the tray icon + menu (one more moving part not
needed yet), and the telemetry store's exponential backoff is now a fixed
3s retry, matching the same simplification made to continuum-proxy's
uplink client.

Fixed two real TS bugs while typechecking apps/web for the first time
(missing @types/node for nuxt.config.ts's process.env access, untyped
useFetch call inferring 'never'). Verified: cargo check (desktop),
vue-tsc --noEmit (web + ui packages) all clean.

apps/web/stores/telemetry.ts

@@ -14,15 +14,15 @@ interface TelemetryState {
   socket: WebSocket | null;
   connected: boolean;
   printers: Record<string, PrinterTelemetry>;
-  reconnectAttempt: number;
 }
 
+const RECONNECT_DELAY_MS = 3_000;
+
 export const useTelemetryStore = defineStore("telemetry", {
   state: (): TelemetryState => ({
     socket: null,
     connected: false,
     printers: {},
-    reconnectAttempt: 0,
   }),
 
   getters: {
@@ -48,7 +48,6 @@ export const useTelemetryStore = defineStore("telemetry", {
 
       socket.onopen = () => {
         this.connected = true;
-        this.reconnectAttempt = 0;
       };
 
       socket.onmessage = (event) => {
@@ -65,9 +64,7 @@ export const useTelemetryStore = defineStore("telemetry", {
       socket.onclose = () => {
         this.connected = false;
         this.socket = null;
-        const delay = Math.min(30_000, 1_000 * 2 ** this.reconnectAttempt);
-        this.reconnectAttempt += 1;
-        setTimeout(() => this.connect(), delay);
+        setTimeout(() => this.connect(), RECONNECT_DELAY_MS);
       };
 
       socket.onerror = () => {