fix(cli): address PR review feedback from miguel-heygen

- flushSync: use detached spawn + unref() instead of execFileSync,
  so process.exit() paths don't block up to 5s on slow networks
- showTelemetryNotice: persist notice flag BEFORE printing/tracking,
  so users are never tracked without having seen the disclosure
- Config dir: set mode 0o700 on ~/.hyperframes/ directory (was umask default)
- $ip: null comment: clarify this is belt-and-suspenders with server-side discard
- shouldTrack: update comment — phc_ prefix check is a safety net, not dead code
- env.ts: add comment explaining try/catch fail-safe defaults to production
- init.ts: consistently call trackInitTemplate after scaffoldProject in both paths

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

packages/cli/src/telemetry/config.ts

@@ -69,7 +69,7 @@ export function readConfig(): HyperframesConfig {
  */
 export function writeConfig(config: HyperframesConfig): void {
   try {
-    mkdirSync(CONFIG_DIR, { recursive: true });
+    mkdirSync(CONFIG_DIR, { recursive: true, mode: 0o700 });
     writeFileSync(CONFIG_FILE, JSON.stringify(config, null, 2) + "\n", { mode: 0o600 });
     cachedConfig = { ...config };
   } catch {