feat(schema): v2.0.0 extension schema — citations, provenance, schema_version

[HartreeY]

• Relaxed "version_constraint" as a required field for dependencies: it's more user-friendly to program the newest version to be tried automatically
• Removed the "compatibility" field as a duplicate of "version_constraint"
• Standardized orthography and some descriptions
• Left the "tools" field in as a good place to describe the tools to the user, but changed "description" to "desc" in "tools"->"items" just in case the "description" field is hard-coded to be the unmodifiable meta-description of the fields themselves
• Implemented "citations", "hatch_schema_version" and "provenance" largely in the format proposed by Eliott
• Relaxed "license" and "tags" in requirements
• "author" -> "authors"; made "authors" stricter with "minItems": 1
• Reimplemented "name"
• Added "digest" to "docker" (left "version_constraint" as human-friendly alt.)
• Docker image name, as well as system.name are now less restrictive
• Added descriptions to "tools" and "documentation"
• Increased description.maxLength to 200
• |version" now validates SemVer
• Docker version_constraint replaced with tag
• Added additionalProperties: false to nested objects where strictness is helpful`

Assumed the following fields would be programmatically picked up from the Official MCP metadata:
"name": "",
"version": "...",
"description": "..."
The rest of the fields should be transmitted inside _meta.io.modelcontextprotocol.registry/publisher-provided.