refactor: consolidate PNG encoder and safeParseJson utilities (#12457)

- Create shared PNG encoder module (src/media/png-encode.ts)

- Refactor qr-image.ts and live-image-probe.ts to use shared encoder

- Add safeParseJson to utils.ts and plugin-sdk exports

- Update msteams and pairing-store to use centralized safeParseJson

src/utils.ts

@@ -31,6 +31,17 @@ export function escapeRegExp(value: string): string {
   return value.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
 }
 
+/**
+ * Safely parse JSON, returning null on error instead of throwing.
+ */
+export function safeParseJson<T>(raw: string): T | null {
+  try {
+    return JSON.parse(raw) as T;
+  } catch {
+    return null;
+  }
+}
+
 export type WebChannel = "web";
 
 export function assertWebChannel(input: string): asserts input is WebChannel {