feat: implement app-side telemetry sender

Add the shared telemetry sender, wire the CLI/server emit points,
and cover the config and completion behavior with tests.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

packages/shared/src/telemetry/state.ts

@@ -0,0 +1,31 @@
+import { randomUUID, randomBytes } from "node:crypto";
+import { existsSync, mkdirSync, readFileSync, writeFileSync } from "node:fs";
+import path from "node:path";
+import type { TelemetryState } from "./types.js";
+
+export function loadOrCreateState(stateDir: string, version: string): TelemetryState {
+  const filePath = path.join(stateDir, "state.json");
+
+  if (existsSync(filePath)) {
+    try {
+      const raw = readFileSync(filePath, "utf-8");
+      const parsed = JSON.parse(raw) as TelemetryState;
+      if (parsed.installId && parsed.salt) {
+        return parsed;
+      }
+    } catch {
+      // Corrupted state file — recreate
+    }
+  }
+
+  const state: TelemetryState = {
+    installId: randomUUID(),
+    salt: randomBytes(32).toString("hex"),
+    createdAt: new Date().toISOString(),
+    firstSeenVersion: version,
+  };
+
+  mkdirSync(stateDir, { recursive: true });
+  writeFileSync(filePath, JSON.stringify(state, null, 2) + "\n", "utf-8");
+  return state;
+}