feat: add resources for listing specs in the registry and get a summary for a specific one

[yelizhenden-mdb]

Proposed changes

Two new MCP resources registered in the server:

• openapi://specs — lists all specs loaded in the registry (returns alias, sourceType, and filePath per spec)
• openapi://specs/{alias} — returns a structural overview of a single spec: title, description, stats (paths, operations, schemas, tags), latestStableVersion, availableVersions, hasPreview, hasUpcoming

Version extraction reuses foascli's ExtractVersions and post-processes the result, so any new stability level foascli adds (e.g. future types) is picked up automatically.

Jira ticket: CLOUDP-393142

Checklist

• I have signed the MongoDB CLA
• I have added tests that prove my fix is effective or that my feature works

Changes to Spectral

• I have read the README file for Spectral Updates

Further comments