feat: improve error handling for empty or malformed prompt and resource files

[lucasdelellis]

Closes #529

This PR extends error handling when loading tool files (PR #528) to resource and prompt files.

• Skips empty files and missing default exports with clear, friendly warnings
• Includes the file path in error messages for invalid resource and prompt implementations
• Preserves full stack traces for real syntax/import errors
• Adds a startup summary for skipped tools
• Avoids repeated warning spam

Note: This contribution follows the same pattern as #528 to maintain code consistency, but it might be worth extracting the duplicated logic from the different loaders into a single shared utility.

[greptile-apps]

PR author is not in the allowed authors list.

[vercel]

@lucasdelellis is attempting to deploy a commit to the xmcp Team on Vercel.

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[0xKoller]

Hi @lucasdelellis , closing this PR.

You can learn more #529