feat(legal): imprint & privacy notices, "Über MindSift"

- LEGAL_IMPRINT_/LEGAL_PRIVACY_ URL and Markdown (inline or *_FILE);
  only http(s) URLs accepted
- /auth/status exposes legal info; public GET /legal/{imprint|privacy}
- Links on login/setup screen and in the settings footer: URL opens a new
  tab, Markdown a reading modal; hidden when nothing is configured
- "Über MindSift" modal (version, license, repository) in settings and help
- Docs and compose/env examples

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/api/server_test.go

@@ -1366,3 +1366,42 @@ func TestFirstBootSetupWithSampleData(t *testing.T) {
 		t.Fatalf("expected sample notes and task lists, got %d notes, %d task lists", len(docs), len(lists))
 	}
 }
+
+// Impressum and Datenschutz must be reachable without login; unset texts stay hidden.
+func TestLegalTextsArePublic(t *testing.T) {
+	dbPath := filepath.Join(t.TempDir(), "legal.db")
+	store, err := storage.NewStore(dbPath)
+	if err != nil {
+		t.Fatalf("NewStore: %v", err)
+	}
+	defer store.Close()
+	cfg := &config.Config{Port: "8080", DatabasePath: dbPath, JWTSecret: "test-jwt-secret-key",
+		Legal: config.LegalTexts{ImprintContent: "# Impressum\nMax Muster", PrivacyURL: "https://example.org/datenschutz"}}
+	router := NewServer(cfg, store, ws.NewHub(), nil).Router()
+
+	rec := httptest.NewRecorder()
+	router.ServeHTTP(rec, httptest.NewRequest(http.MethodGet, "/api/v1/auth/status", nil))
+	var st struct {
+		Legal struct {
+			ImprintURL        string `json:"imprintUrl"`
+			HasImprintContent bool   `json:"hasImprintContent"`
+			PrivacyURL        string `json:"privacyUrl"`
+			HasPrivacyContent bool   `json:"hasPrivacyContent"`
+		} `json:"legal"`
+	}
+	_ = json.Unmarshal(rec.Body.Bytes(), &st)
+	if !st.Legal.HasImprintContent || st.Legal.HasPrivacyContent || st.Legal.PrivacyURL != "https://example.org/datenschutz" {
+		t.Fatalf("unexpected legal status: %+v", st.Legal)
+	}
+
+	rec = httptest.NewRecorder()
+	router.ServeHTTP(rec, httptest.NewRequest(http.MethodGet, "/api/v1/legal/imprint", nil))
+	if rec.Code != http.StatusOK || !strings.Contains(rec.Body.String(), "Max Muster") {
+		t.Fatalf("imprint without login: %d %s", rec.Code, rec.Body.String())
+	}
+	rec = httptest.NewRecorder()
+	router.ServeHTTP(rec, httptest.NewRequest(http.MethodGet, "/api/v1/legal/privacy", nil))
+	if rec.Code != http.StatusNotFound {
+		t.Fatalf("privacy without text should be 404, got %d", rec.Code)
+	}
+}