docs: fix MCP dependency for docs server setup

[xblwh]

Fixes #2219.

Add --with "mcp<2" to the Antigravity, Claude Code, and Cursor setup examples, and explain the compatibility constraint. mcpdoc 0.0.10 allows MCP 2.x to be installed but still imports the MCP 1.x FastMCP API, causing startup to fail.

Validation

• mkdocs build --strict passed with output directed outside the checkout.
• Parsed both JSON configs and confirmed all three snippets produce the same uvx arguments.
• Reproduced the original FastMCP import error; the constrained command starts successfully.
• Verified MCP initialize and tools/list, including list_doc_sources and fetch_docs.
• git diff --check passed.

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[joefernandez]

Technical review report

• Review Score: 99
• Overall assessment: 🟢 Low Risk
• Summary reasoning: The change fixes a real, currently-reproducible breakage in the documented mcpdoc setup commands, and the fix is correct in all three places it appears. I reproduced both the failure and the fix locally. The only issue is the placement of the new explanatory sentence.
• Recommended action: Approve with one optional change. The technical claim and the pin are verified correct; the only nit is that the explanatory sentence at line 46 appears before the reader has seen mcp<2 in any config block, so it reads as an unexplained forward reference.
• Number of lines changed: XS, 9
• Number of files changed: 1

Verification performed

The fix is correct and necessary. As of today, uvx --from mcpdoc mcpdoc ... — the command the docs shipped before this PR — fails outright:

File ".../mcpdoc/main.py", line 9, in <module>
    from mcp.server.fastmcp import FastMCP
ModuleNotFoundError: No module named 'mcp.server.fastmcp'. This is mcp 2.x, where FastMCP
was renamed to MCPServer ... or pin 'mcp<2' to keep running v1 code.

Root cause chain, all confirmed against upstream source:

• mcpdoc 0.0.10 declares mcp[cli]>=1.4.1 with no upper bound — pyproject.toml:11, so uvx resolves the newest mcp (2.2.0, released 2026-09-07).
• mcpdoc still imports the v1 API — mcpdoc/main.py:9: from mcp.server.fastmcp import FastMCP.
• mcp 2.x turned that module into a tombstone that raises on import — src/mcp/server/fastmcp.py:16. The upstream error message itself recommends exactly the mcp<2 pin this PR adds.

With the PR's command, the server resolves mcp 1.30.0 and completes an MCP initialize handshake over stdio, returning "serverInfo":{"name":"llms-txt"}. So the claim at lines 46-47 — "keeps mcpdoc compatible with the MCP 1.x FastMCP API it currently uses" — is accurate, including the hedge "currently".

Other checks:

• Argument ordering is valid uv syntax in all three spots: --with is a uvx option and correctly precedes the mcpdoc command token (L67-68, L86, L106-107).
• The Claude Code one-liner correctly quotes "mcp<2"; unquoted it would be a shell redirection. The two JSON args arrays are not shell-parsed, so the bare "mcp<2" string there is right.
• No mcpdoc references elsewhere in the repo were missed — it appears only in this file.
• No ADK repository (adk-python, adk-js, adk-go, adk-java, adk-kotlin) surface is touched, so there is no unreleased-code exposure.

🟢 Low risk items

• docs/tutorials/coding-with-ai.md:46-47: the sentence explaining mcp<2 sits directly under the "ADK Docs MCP Server" heading, before any config block containing mcp<2. A reader meets the justification before the thing being justified. Suggest making it a note that reads forward, so it works wherever the reader lands:

  ```suggestion
  !!! note "Why `mcp<2`?"
  
      The setup commands below pin `mcp<2`. The `mcpdoc` package still imports
      the MCP 1.x `FastMCP` API, which was renamed in MCP 2.x, so without the
      pin the server fails to start.

[joefernandez]

Thanks for the update!