fix: handle non-JSON files and invalid JSON

[Devansh-567]

Summary

This PR improves the robustness of the repository's annotation validation scripts by handling two cases that currently result in uncaught exceptions.

• bin/annotate-specification-links now uses version_urls.get(kind) instead of direct dictionary indexing, allowing the existing error-handling path for unknown specification kinds to execute.
• bin/annotation-tests.ts now only processes .json files and reports invalid JSON with a readable per-file error instead of aborting with an uncaught exception.

Changes

bin/annotate-specification-links

• Replace version_urls[kind] with version_urls.get(kind).

This ensures that unknown specification kinds are handled by the existing None check rather than raising a KeyError.

bin/annotation-tests.ts

• Only process files ending with .json.
• Wrap JSON.parse in a try/catch.
• Report invalid JSON as a per-file validation error and continue validating the remaining files.

This prevents unrelated files (such as README.md or editor temporary files) or malformed JSON from terminating the validation script with an uncaught exception.

Why

Both changes make the validation scripts more resilient while preserving their behavior for valid inputs.

• Unknown specification kinds now follow the existing error-reporting path instead of raising a KeyError.
• Annotation test validation now ignores non-JSON files and reports malformed JSON with a clear error message instead of failing with a stack trace.