docs(mcp-openapi): document x-zilla-mcp extension and tools.title/annotations

[jfallows]

Summary

• The mcp-openapi reference page's options.tools section only documented the description/summary/input/output overrides — it never mentioned the x-zilla-mcp OpenAPI vendor extension (title/description/annotations) that mcp-kafka-connect and mcp-schema-registry already use, via an overlay, to supply real MCP tool metadata for their bundled specs without an authored options.tools entry or editing the vendored OpenAPI document.
• It also never documented options.tools.title or options.tools.annotations, even though both are real, existing config fields alongside description/summary/input/output.
• Adds:
  • tools.title and tools.annotations (with its four hint children readOnlyHint/destructiveHint/idempotentHint/openWorldHint) property docs.
  • Corrects tools.description's precedence text to include the x-zilla-mcp.description fallback layer that sits between the authored override and the operation's native description/id.
  • An info callout (placed after specs.overlay, since overlay is the mechanism used to inject it) documenting the x-zilla-mcp operation extension's shape and precedence, cross-linking to mcp-kafka-connect/mcp-schema-registry as the in-tree usage example.

Test plan

• pnpm lint — no new violations introduced (verified the changed file specifically has zero reported issues; all other reported issues are pre-existing, in unrelated files)
• pnpm check-schema — no output referencing mcp-openapi (the tracked .check-schema/zilla-schema.json only defines the base mcp binding type, predating mcp-openapi/mcp-http/mcp-kafka entirely — same pre-existing gap noted in docs(mcp): add mcp-kafka-connect and mcp-schema-registry binding reference #417, not introduced by this change)
• Verified the documented precedence chains directly against the current binding-mcp-openapi source on zilla's develop branch (McpOpenapiCompositeGenerator.toolTitle/toolDescription/toolAnnotations, McpEx)
• Visual check of the rendered page via pnpm dev (not run in this environment)

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Generated by Claude Code

[jfallows]

LGTM