✨ 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/src/tools/mod.rs

@@ -0,0 +1,6 @@
+//! Tool implementations — one module per tool.
+
+pub mod schema;
+// pub mod doctor;   // wired in Plan Task 5
+// pub mod search;   // wired in Plan Task 6
+// pub mod ask;      // wired in Plan Task 7

crates/kebab-mcp/src/tools/schema.rs

@@ -0,0 +1,22 @@
+//! `schema` tool — wraps `kebab_app::schema_with_config`.
+//! Input: {} (no args). Output: schema.v1 JSON.
+
+use rmcp::model::CallToolResult;
+use serde::{Deserialize, Serialize};
+use schemars::JsonSchema;
+
+use crate::error::{to_tool_error, to_tool_success};
+use crate::state::KebabAppState;
+
+#[derive(Debug, Default, Deserialize, Serialize, JsonSchema)]
+pub struct SchemaInput {}
+
+pub fn handle(state: &KebabAppState, _input: SchemaInput) -> CallToolResult {
+    match kebab_app::schema_with_config(&state.config) {
+        Ok(report) => match serde_json::to_string(&report) {
+            Ok(json) => to_tool_success(json),
+            Err(e) => to_tool_error(&anyhow::anyhow!(e)),
+        },
+        Err(e) => to_tool_error(&e),
+    }
+}