Add filesystem capability seam and tools

packages/fs/tool-fs/tsdown.config.ts

@@ -0,0 +1,18 @@
+import { defineConfig } from 'tsdown'
+
+/**
+ * tool-fs exposes one package root plus one entry per tool plugin, so each tool
+ * can be loaded or replaced independently as a subpath plugin
+ * (`@deepseek-ai/dsh-tool-fs/read`, `/write`, `/edit`). The root tsdown config
+ * only auto-discovers `src/index.ts`, so the subpath entries are declared here.
+ */
+export default defineConfig({
+  entry: ['src/index.ts', 'src/read.ts', 'src/write.ts', 'src/edit.ts'],
+  outDir: 'lib',
+  format: ['esm'],
+  platform: 'node',
+  target: 'es2024',
+  fixedExtension: false,
+  dts: false,
+  clean: false,
+})