feat(create_project): add dispatch_allow to inject .dispatch-allow (#43)

Optional dispatch_allow bool (default false). When true, inject a
.dispatch-allow file at repo root on the resolved default branch after
substitution, marking the new project dispatch-eligible (dispatch#3)
without a manual follow-up commit.

Rides the existing upsertRetry path so injection inherits the infra#179
branch-readiness / partial_failure handling; a stalled injection degrades
exactly like substitution. Reported in files_substituted. false/omitted
is byte-for-byte unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/tools/create_project_from_template_test.go

@@ -226,6 +226,38 @@ func TestCreateProject_WriteFailure_PartialFailure(t *testing.T) {
 	assert.Contains(t, out.PartialFailure, "go.mod")
 }
 
+// dispatch_allow injects a .dispatch-allow file (dispatch#3) only when true.
+func TestCreateProject_DispatchAllow(t *testing.T) {
+	tests := []struct {
+		name     string
+		argsJSON string
+		wantFile bool
+	}{
+		{"true injects .dispatch-allow", `{"owner":"mathias","name":"new-svc","dispatch_allow":true}`, true},
+		{"false does not inject", `{"owner":"mathias","name":"new-svc","dispatch_allow":false}`, false},
+		{"omitted does not inject", `{"owner":"mathias","name":"new-svc"}`, false},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			files := map[string]string{"go.mod": "module __MODULE_PATH__\n"}
+			f := newFakeTemplateServer(files, "main")
+			srv := httptest.NewServer(f.handler(t, "template-go-agent", "new-svc"))
+			defer srv.Close()
+
+			out := callTool(t, srv.URL, "template-go-agent", tc.argsJSON)
+			require.Empty(t, out.PartialFailure)
+			if tc.wantFile {
+				assert.Contains(t, out.FilesSubstituted, ".dispatch-allow")
+				assert.Contains(t, f.puts, ".dispatch-allow")
+				assert.Contains(t, f.putBodies[".dispatch-allow"], "dispatch#3")
+			} else {
+				assert.NotContains(t, out.FilesSubstituted, ".dispatch-allow")
+				assert.NotContains(t, f.puts, ".dispatch-allow")
+			}
+		})
+	}
+}
+
 // ── guardrails unchanged by the rewrite ──────────────────────────────────────
 
 func TestCreateProject_NameRegexFailure(t *testing.T) {