docs/MCP.md describes the feed and returns tools: `feed_chips`, `next_steps`, `returns`, `thought` #5281

Intent: a person or harness reading docs/MCP.md finds every tool the server lists. Today these tools answer in tools/list but have no row in the docs/MCP.md table.

Done:

• [ ] docs/MCP.md's tool table has one row for each of feed_chips, next_steps, returns, thought, beside its neighbours by theme, saying in plain words what it does and ticking writes when it changes anything, matching the tool's description and handler in src/http/mcp.ts
• [ ] if test/mcp-docs.test.ts exists by then (another issue adds it with an allowlist of undocumented tools, one name per line), these names leave its allowlist; otherwise nothing else changes
• [ ] no source file changes

Files: docs/MCP.md, and the allowlist lines in test/mcp-docs.test.ts if it exists. Other issues add other rows in parallel: add only these.