feat: add mutation tools and help command for v0.0.4

- Add envsitter_add, envsitter_set, envsitter_unset, envsitter_delete tools
- Add envsitter_help tool with comprehensive usage guide for agents
- Change blocking to silent mode (error messages only, no toasts)
- Bump envsitter dependency to ^0.0.4
- Update README with new tools and envsitter library reference
- Update CHANGELOG for v0.0.4

test/envsitter-guard.hook.test.ts

@@ -105,12 +105,12 @@ test("strips @ prefix in filePath", async () => {
     );
 });
 
-test("toasts are throttled", async () => {
+test("blocking is silent (no toasts)", async () => {
     const worktree = await createTmpDir();
     const { hook, calls } = await getBeforeHook({ directory: worktree, worktree });
 
     await assert.rejects(() => hook({ tool: "read", sessionID: "s", callID: "c" }, { args: { filePath: ".env" } }));
     await assert.rejects(() => hook({ tool: "read", sessionID: "s", callID: "c" }, { args: { filePath: ".env" } }));
 
-    assert.equal(calls.showToast, 1);
+    assert.equal(calls.showToast, 0, "should not show toasts, only throw errors");
 });