fix(deps): pin mcp<2 to end the prod crashloop, and smoke-test the image

requirements.txt asked for `mcp[fastmcp]>=1.0.0` with no upper bound.
mcp 2.0.0 (2026-07-28) removed `mcp.server.fastmcp` — renamed FastMCP to
MCPServer under mcp.server.mcpserver — and dropped the [fastmcp] extra.
docs_mcp/server.py:28 still imports the 1.x path.

The 2026-07-01 image predated 2.0.0, so it resolved to 1.x and ran fine.
The 2026-09-01 rebuild resolved to mcp 2.1.1, and the container has been
crash-looping ever since:

  File "/app/docs_mcp/server.py", line 28, in <module>
      from mcp.server.fastmcp import FastMCP
  ModuleNotFoundError: No module named 'mcp.server.fastmcp'

That is nine days of seed-mcp being down for Drawbar's advisor. Same
failure took zerto-docs down on 2026-08-11; crop-chem-docs and
opsramp-docs were pinned then, seed-mcp was missed.

This is a ceiling to restore service, not the destination — the 2.x port
lands separately. It also adds the guard that would have caught this: the
build now runs `python -c "import docs_mcp.server"` inside the freshly
built image and refuses to push if that fails. Import is side-effect-free
(lazy singletons), so the check needs no Ollama or Chroma.

Still unpinned and due to break on their next rebuild: morpheus-docs,
hvm-docs.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01FnVuG79cYPcRLTp4pC8ujR

requirements.txt

@@ -1,5 +1,5 @@
 # MCP server
-mcp[fastmcp]>=1.0.0
+mcp[fastmcp]>=1.0.0,<2  # 2.x removed mcp.server.fastmcp (FastMCP -> MCPServer); see docs_mcp/server.py
 pydantic>=2.0
 httpx>=0.27