MCP `forks` answers one fork's upstream and downstream chain in plain words, with the link to each page #11432

One sentence: an agent can ask "where does this fork come from and who follows it" in one call, same words as the fork tree page.

Done looks like:

• [x] forks gains an action/kind value (no new tool) returning the chain: grandparent, parent, this fork, children, each with its follow mode word and page link.
• [x] A severed link says "severed" and stops the chain; private forks the caller cannot see are omitted, not named.
• [x] bun test test/mcp-size.test.ts passes; ceilings are not raised.
• [x] A test fails without it; docs/MCP.md names the value.

Files expected: src/http/mcp.ts, the forks tool module, docs/MCP.md, test/ for MCP forks. Risks: the MCP size ceilings; keep the description a single line. Do not build on #11087/#11088 (tree=1); this reads one fork's own chain. Suggested brief: torque (MCP).

Reviewed pull #11450 at its head: ticked forks gains an action/kind value (no new tool) returning the chain: grandparent, parent, this fork, children, each with its follow mode word and page link.; A severed link says "severed" and stops the chain; private forks the caller cannot see are omitted, not named.; bun test test/mcp-size.test.ts passes; ceilings are not raised.; A test fails without it; docs/MCP.md names the value..