Expand site-absolute spec links in generated docstrings to full URLs

[maxisbey]

The Deploy Docs workflow on main is failing since #2849: the strict mkdocs build aborts with 54 warnings, all of them mkdocs flagging the site-absolute link (/specification/2025-11-25/basic/index#meta) in the generated api/mcp/types/v2025_11_25 API reference page (failing run).

Motivation and Context

The vendored schema descriptions link to spec pages with site-absolute paths (they're written for modelcontextprotocol.io). gen_surface_types.py copies them verbatim into the per-version package docstrings, so the rendered API reference ends up with links that don't resolve from the SDK docs site, and validation.absolute_links: warn + strict: true in mkdocs.yml turns each occurrence into a build failure. The docs site can't deploy until this is fixed.

This PR adds one post-processing step to the generator that expands site-absolute markdown link targets to full https://modelcontextprotocol.io/... URLs, and regenerates the 2025-11-25 package (54 docstring lines change, nothing else). The 2026-07-28 package has no such links and is byte-identical after regeneration. The rewrite matches any site-absolute link target rather than just /specification/, so a future schema vendoring that links to other spec-site pages won't reintroduce the failure.

How Has This Been Tested?

• uv run --frozen --group codegen python scripts/gen_surface_types.py --check passes (no drift between the generator and the committed packages).
• uv run --frozen --group docs mkdocs build (strict mode) now exits 0 with zero absolute-link warnings; before the change it aborted with 54.
• The built api/mcp/types/v2025_11_25/index.html contains 54 href="https://modelcontextprotocol.io/specification/2025-11-25/basic/index#meta" links and no site-absolute ones.

The "MkDocs 2.0 is incompatible with Material for MkDocs" notice in the build log is unrelated: it's informational output from mkdocs-material 9.7.x (mkdocs is locked at 1.6.1) and doesn't trip strict mode.

Breaking Changes

None — only docstrings in a generated internal module and the generator script change.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

A separate question this PR doesn't take a position on: whether the internal, versioned wire-shape packages (mcp.types.v2025_11_25, mcp.types.v2026_07_28) should appear in the rendered API reference at all — docs/hooks/gen_ref_pages.py currently publishes every package under src/. Even if they're later excluded, the full URLs are still the right thing for IDE tooltips and help() output.

_{AI Disclaimer}