✨ feat(kebab-cli): kebab mcp subcommand (fb-30)

Wires kebab_mcp::serve_stdio into kebab-cli. `--config <path>` honored
via the established Config::load pattern.

Updated serve_stdio signature to (Config, Option<PathBuf>) so the doctor
tool's path-aware behavior works correctly via KebabAppState.

Smoke test spawns the binary + sends initialize + initialized +
tools/list over stdin, asserts 4 tools returned. Confirms the MCP
server boots end-to-end via the real binary (rmcp 1.6 has no
in-memory test transport, so this is the only end-to-end assertion).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/kebab-cli/Cargo.toml

@@ -27,6 +27,8 @@ kebab-eval = { path = "../kebab-eval" }
 # enforces the §8 boundary in its own Cargo.toml; kb-cli just
 # launches it.
 kebab-tui    = { path = "../kebab-tui" }
+# p9-fb-30: MCP stdio server. `Cmd::Mcp` delegates entirely to this crate.
+kebab-mcp    = { path = "../kebab-mcp" }
 anyhow       = { workspace = true }
 serde        = { workspace = true }
 serde_json   = { workspace = true }