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/agents/pi-embedded-helpers/errors.ts

@@ -25,7 +25,6 @@ export function isContextOverflowError(errorMessage?: string): boolean {
     lower.includes("exceeds model context window") ||
     (hasRequestSizeExceeds && hasContextWindow) ||
     lower.includes("context overflow:") ||
-    lower.includes("context overflow") ||
     (lower.includes("413") && lower.includes("too large"))
   );
 }