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/package.json

@@ -21,6 +21,7 @@
     "vue-router": "^4.4.3"
   },
   "devDependencies": {
+    "@types/node": "^22.7.4",
     "typescript": "^5.6.2"
   }
 }

apps/web/pages/index.vue

@@ -2,10 +2,17 @@
 import { PrinterCard } from "@continuum/ui";
 import { useTelemetryStore } from "~/stores/telemetry";
 
+interface Printer {
+  id: string;
+  name: string;
+  model: string;
+  farmId: string;
+}
+
 const telemetry = useTelemetryStore();
 const config = useRuntimeConfig();
 
-const { data: printers } = await useFetch(`${config.public.apiBase}/printers`, {
+const { data: printers } = await useFetch<Printer[]>(`${config.public.apiBase}/printers`, {
   headers: useRequestHeaders(["cookie"]),
 });
 </script>

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 = () => {