feat: core agent tools (fs, search, shell)

src/types.ts

@@ -0,0 +1,15 @@
+export interface FileEntry {
+  name: string;
+  kind: "file" | "dir";
+}
+
+export interface SearchResult {
+  path: string;
+  matches: number;
+}
+
+export interface CommandOutput {
+  stdout: string;
+  stderr: string;
+  exit_code: number;
+}