✨ feat(kebab-mcp): doctor tool (fb-30)

Second tool — `doctor` (no input args, returns doctor.v1 JSON via
kebab_app::doctor_with_config_path). Mirrors schema tool's manual-dispatch
pattern: Tool::new entry in list_tools, match arm in call_tool, per-tool
module in tools/doctor.rs.

doctor_with_config_path takes Option<&Path> (not &Config), so KebabAppState
is extended with config_path: Option<PathBuf>. All existing callers
(initialize.rs, tools_call_schema.rs, serve_stdio_async) pass None for now;
Plan Task 10 (Cmd::Mcp wiring) will thread the actual --config path through.
doctor_with_config falls back to XDG default when config_path is None —
same behavior as bare `kebab doctor`.

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

crates/kebab-mcp/tests/tools_call_doctor.rs

@@ -0,0 +1,50 @@
+//! Integration: tools/call name=doctor — returns doctor.v1.
+
+use kebab_config::Config;
+use kebab_mcp::{KebabAppState, KebabHandler};
+use rmcp::model::RawContent;
+
+#[tokio::test]
+async fn doctor_tool_returns_doctor_v1_json() {
+    let dir = tempfile::tempdir().unwrap();
+    let mut cfg = Config::defaults();
+    cfg.storage.data_dir = dir.path().join("data").to_string_lossy().into_owned();
+    cfg.workspace.root = dir.path().join("notes").to_string_lossy().into_owned();
+    cfg.models.embedding.provider = "none".to_string();
+    cfg.models.embedding.dimensions = 0;
+    std::fs::create_dir_all(&cfg.workspace.root).unwrap();
+
+    // Pass None for config_path — doctor falls back to XDG default probe
+    // (path won't exist in the tempdir, which is fine; doctor reports it
+    // as missing / error rather than panicking).
+    let state = KebabAppState::new(cfg, None);
+    let handler = KebabHandler::new(state);
+
+    let result = kebab_mcp::tools::doctor::handle(
+        handler.state(),
+        kebab_mcp::tools::doctor::DoctorInput::default(),
+    );
+
+    let content = result
+        .content
+        .first()
+        .expect("expected at least one content item");
+
+    let text = match &content.raw {
+        RawContent::Text(t) => &t.text,
+        other => panic!("expected text content, got {other:?}"),
+    };
+
+    let v: serde_json::Value = serde_json::from_str(text).unwrap();
+    assert_eq!(
+        v.get("schema_version").and_then(|s| s.as_str()),
+        Some("doctor.v1"),
+        "unexpected schema_version in: {v}"
+    );
+    // `ok` boolean must be present (value may be false in CI where Ollama
+    // is not reachable — that's expected and acceptable).
+    assert!(
+        v.get("ok").and_then(|b| b.as_bool()).is_some(),
+        "`ok` field missing in doctor.v1 response: {v}"
+    );
+}