feat(0130): kanban_cpp v2 — backend Go + 5 registry parser fns + epic/sub-issues

Registry (issue 0130a):
- 5 fns infra: parse_issue_md, write_issue_md, scan_issues_dir,
  scan_flows_dir, watch_dir_fsnotify
- 3 tipos: Issue, Flow, FsEvent
- Tests round-trip + scan reales + watcher fsnotify (all PASS)
- Capability group 'kanban' nuevo (docs/capabilities/kanban.md)

Apps:
- apps/kanban_cpp/ (sub-repo) — frontend ImGui: board drag-drop,
  flows, filters, detail con CSV editors
- apps/kanban_cpp/backend/ — Go service port 8487: REST + SSE +
  fsnotify watcher, parser bidireccional MD<->SQLite cache

Issues:
- dev/issues/0130-kanban-cpp-v2.md (epic)
- 0130a parser, 0130b backend, 0130c frontend

CMakeLists.txt: add_subdirectory apps/kanban_cpp (registrado por
init_cpp_app scaffolder).

End-to-end verde: backend devuelve 189 issues + 9 flows; PATCH a
/api/issues/{id} reescribe .md (solo frontmatter, body intacto);
frontend --self-test exit 0; tests Go infra 5/5 PASS.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

functions/infra/write_issue_md_test.go

@@ -0,0 +1,92 @@
+package infra
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestWriteIssueMd(t *testing.T) {
+	root := registryRoot()
+
+	t.Run("round-trip parse-write-parse preserva struct", func(t *testing.T) {
+		fixturePath := filepath.Join(root, "functions", "infra", "testdata", "issue_fixture.fixture")
+
+		// Parse original
+		iss1, body1, err := ParseIssueMd(fixturePath)
+		if err != nil {
+			t.Fatalf("ParseIssueMd: %v", err)
+		}
+
+		// Write a TempDir
+		tmpPath := filepath.Join(t.TempDir(), "issue_roundtrip.md")
+		if err := WriteIssueMd(tmpPath, iss1, body1); err != nil {
+			t.Fatalf("WriteIssueMd: %v", err)
+		}
+
+		// Parse de nuevo
+		iss2, body2, err := ParseIssueMd(tmpPath)
+		if err != nil {
+			t.Fatalf("ParseIssueMd after write: %v", err)
+		}
+
+		// Comparar campos (ignorar FilePath y MtimeNs que son runtime)
+		if iss1.ID != iss2.ID {
+			t.Errorf("ID: %q != %q", iss1.ID, iss2.ID)
+		}
+		if iss1.Title != iss2.Title {
+			t.Errorf("Title: %q != %q", iss1.Title, iss2.Title)
+		}
+		if iss1.Status != iss2.Status {
+			t.Errorf("Status: %q != %q", iss1.Status, iss2.Status)
+		}
+		if iss1.Flow != iss2.Flow {
+			t.Errorf("Flow: %q != %q", iss1.Flow, iss2.Flow)
+		}
+		if len(iss1.Domain) != len(iss2.Domain) {
+			t.Errorf("Domain len: %d != %d", len(iss1.Domain), len(iss2.Domain))
+		}
+		if len(iss1.Depends) != len(iss2.Depends) {
+			t.Errorf("Depends len: %d != %d", len(iss1.Depends), len(iss2.Depends))
+		}
+		if len(iss1.Tags) != len(iss2.Tags) {
+			t.Errorf("Tags len: %d != %d", len(iss1.Tags), len(iss2.Tags))
+		}
+
+		// El body debe preservarse exactamente
+		if string(body1) != string(body2) {
+			t.Errorf("body mismatch:\ngot:  %q\nwant: %q", string(body2), string(body1))
+		}
+	})
+
+	t.Run("archivo resultante empieza con ---", func(t *testing.T) {
+		iss := Issue{
+			ID:     "0001",
+			Title:  "Test issue",
+			Status: "pendiente",
+		}
+		tmpPath := filepath.Join(t.TempDir(), "test.md")
+		if err := WriteIssueMd(tmpPath, iss, []byte("# Body\n")); err != nil {
+			t.Fatalf("WriteIssueMd: %v", err)
+		}
+		data, _ := os.ReadFile(tmpPath)
+		if len(data) < 4 || string(data[:4]) != "---\n" {
+			t.Errorf("file should start with '---\\n', got: %q", string(data[:min(10, len(data))]))
+		}
+	})
+
+	t.Run("error en path inexistente", func(t *testing.T) {
+		iss := Issue{ID: "0001", Title: "x", Status: "pendiente"}
+		err := WriteIssueMd("/nonexistent/dir/issue.md", iss, []byte("body"))
+		if err == nil {
+			t.Error("expected error writing to nonexistent dir")
+		}
+	})
+}
+
+func min(a, b int) int {
+	if a < b {
+		return a
+	}
+	return b
+}