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

First tool wired — `schema` (no input args, returns schema.v1 JSON
mirroring `kebab schema --json`). Establishes the per-tool module
pattern (crates/kebab-mcp/src/tools/<name>.rs) + error helper that maps
anyhow::Error to MCP CallToolResult.error with error.v1 content.

Dispatch pattern: manual dispatch — explicit `list_tools` + `call_tool`
overrides on `impl ServerHandler for KebabHandler` with a
`match request.name.as_ref()` arm per tool. No proc-macro magic.
Tasks 5-7 should add a new arm + new tools/<name>.rs following the same
pattern; also add a `Tool::new(...)` entry in `list_tools`.

API shapes confirmed from rmcp 1.6 source:
- Content = Annotated<RawContent>; text via `Content::text(s)`; pattern
  match via `&content.raw` → `RawContent::Text(t)` → `t.text`
- CallToolResult::success(Vec<Content>) / ::error(Vec<Content>)
- ListToolsResult::with_all_items(Vec<Tool>)
- schema_for_empty_input() from rmcp::handler::server::common

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

crates/kebab-mcp/tests/tools_call_schema.rs

@@ -0,0 +1,70 @@
+//! Integration: tools/call name=schema — verify response is schema.v1.
+
+use std::fs;
+
+use kebab_config::Config;
+use kebab_core::SourceScope;
+use kebab_mcp::{KebabAppState, KebabHandler};
+use rmcp::model::RawContent;
+
+fn minimal_config(data_dir: &std::path::Path, workspace_root: &std::path::Path) -> Config {
+    let mut cfg = Config::defaults();
+    cfg.storage.data_dir = data_dir.to_string_lossy().into_owned();
+    cfg.storage.model_dir = data_dir
+        .join("models")
+        .to_string_lossy()
+        .into_owned();
+    cfg.workspace.root = workspace_root.to_string_lossy().into_owned();
+    cfg.workspace.exclude.clear();
+    cfg.models.embedding.provider = "none".to_string();
+    cfg.models.embedding.dimensions = 0;
+    cfg
+}
+
+#[tokio::test]
+async fn schema_tool_returns_schema_v1_json() {
+    let dir = tempfile::tempdir().unwrap();
+    let data_dir = dir.path().join("data");
+    let workspace_root = dir.path().join("notes");
+    fs::create_dir_all(&data_dir).unwrap();
+    fs::create_dir_all(&workspace_root).unwrap();
+
+    let config = minimal_config(&data_dir, &workspace_root);
+
+    // Seed kebab.sqlite via 0-file ingest so open_existing succeeds later.
+    let scope = SourceScope {
+        root: workspace_root.clone(),
+        include: vec![],
+        exclude: vec![],
+    };
+    let _ = kebab_app::ingest_with_config(config.clone(), scope, false).unwrap();
+
+    let state = KebabAppState::new(config);
+    let handler = KebabHandler::new(state);
+
+    let result = kebab_mcp::tools::schema::handle(
+        handler.state(),
+        kebab_mcp::tools::schema::SchemaInput::default(),
+    );
+
+    assert!(
+        !result.is_error.unwrap_or(false),
+        "expected isError=false on healthy schema, got {:?}",
+        result
+    );
+
+    let content = result.content.first().expect("expected at least one content item");
+
+    // Content = Annotated<RawContent>; deref to get the inner RawContent.
+    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("schema.v1"),
+        "unexpected schema_version in: {v}"
+    );
+}