feat: organizations decide who sees whom; sharing only by owners

- Server admins manage organizations (one per user); new admin section,
  organization on user creation and invites, setup creates the first one
- Sharing modes private / organizations / open, enforced centrally
  (CanSee, CanShareWith) for directory, all shares and groups; unknown and
  invisible targets give the same error
- Losing visibility (org change, mode change, leaving a group) prunes shares,
  group memberships and task assignments; dry run warns before tightening
- Only owners share; editors can no longer reshare lists or remove others'
  shares; legacy task_lists.team_id and old /organizations endpoints removed
  (FLAW-06, FLAW-10, FLAW-24)
- Schema version: outdated databases are wiped and recreated on start
- Fix setup sample data (createSampleData was ignored); setup and admin
  use a shared ToggleSwitch instead of checkboxes
- Docs: sharing-and-permissions rewritten, ui-patterns, REST, DB, flaws

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

internal/storage/sqlite_test.go

@@ -15,6 +15,7 @@ func TestStoreLifecycle(t *testing.T) {
 	dbPath := filepath.Join(tmpDir, "test_mindsift.db")
 
 	store, err := NewStore(dbPath)
+	openSharing(t, store)
 	if err != nil {
 		t.Fatalf("NewStore failed: %v", err)
 	}
@@ -106,7 +107,7 @@ func TestStoreLifecycle(t *testing.T) {
 	}
 
 	// 6. Test Organizations & Teams
-	org, err := store.CreateOrganization(user.ID, "Mindsift Inc")
+	org, err := store.CreateOrganization("Mindsift Inc")
 	if err != nil || org.ID == "" {
 		t.Fatalf("CreateOrganization failed: %v", err)
 	}
@@ -138,7 +139,7 @@ func TestStoreLifecycle(t *testing.T) {
 	if err != nil || sysSettings.InstanceName == "" {
 		t.Fatalf("GetSystemSettings failed: %v", err)
 	}
-	sysSettings.SharingMode = "teams_only"
+	sysSettings.SharingMode = SharingOpen
 	err = store.UpdateSystemSettings(sysSettings)
 	if err != nil {
 		t.Fatalf("UpdateSystemSettings failed: %v", err)
@@ -179,7 +180,7 @@ func TestStoreLifecycle(t *testing.T) {
 		t.Fatalf("viewer must not delete tasks, got %v", err)
 	}
 	newTitle := "Umbenannt"
-	if _, err := store.UpdateTaskList(user2.ID, taskList.ID, &newTitle, nil, nil, nil, nil, nil); !errors.Is(err, ErrTaskListReadOnly) {
+	if _, err := store.UpdateTaskList(user2.ID, taskList.ID, &newTitle, nil, nil, nil, nil); !errors.Is(err, ErrTaskListReadOnly) {
 		t.Fatalf("viewer must not update task list, got %v", err)
 	}
 	if _, err := store.AddTaskListShare(taskList.ID, "user", user2.ID, "editor", user.ID); err != nil {
@@ -236,6 +237,7 @@ func TestPerUserDocPinning(t *testing.T) {
 	dbPath := filepath.Join(tmpDir, "pin_test.db")
 
 	store, err := NewStore(dbPath)
+	openSharing(t, store)
 	if err != nil {
 		t.Fatalf("NewStore failed: %v", err)
 	}
@@ -312,6 +314,7 @@ func TestEnsureDemoAccountsAndLoginLookup(t *testing.T) {
 	dbPath := filepath.Join(tmpDir, "demo_test.db")
 
 	store, err := NewStore(dbPath)
+	openSharing(t, store)
 	if err != nil {
 		t.Fatalf("NewStore failed: %v", err)
 	}
@@ -368,6 +371,7 @@ func TestFolderManagementAndDeletion(t *testing.T) {
 	dbPath := filepath.Join(tmpDir, "folder_test.db")
 
 	store, err := NewStore(dbPath)
+	openSharing(t, store)
 	if err != nil {
 		t.Fatalf("NewStore failed: %v", err)
 	}
@@ -441,6 +445,7 @@ func TestWorkspaceBlockHashtagsAndDetails(t *testing.T) {
 	dbPath := filepath.Join(tmpDir, "tags_test.db")
 
 	store, err := NewStore(dbPath)
+	openSharing(t, store)
 	if err != nil {
 		t.Fatalf("NewStore failed: %v", err)
 	}
@@ -542,6 +547,7 @@ func TestDatabaseFirstWorkspaceArchitecture(t *testing.T) {
 	dbPath := filepath.Join(tmpDir, "test_db_first.db")
 
 	store, err := NewStore(dbPath)
+	openSharing(t, store)
 	if err != nil {
 		t.Fatalf("NewStore failed: %v", err)
 	}
@@ -692,6 +698,7 @@ func TestBlockListAndDerivedData(t *testing.T) {
 	dbPath := filepath.Join(tmpDir, "tabula_rasa_test.db")
 
 	store, err := NewStore(dbPath)
+	openSharing(t, store)
 	if err != nil {
 		t.Fatalf("NewStore failed: %v", err)
 	}
@@ -752,4 +759,18 @@ func TestBlockListAndDerivedData(t *testing.T) {
 	}
 }
 
-
+// openSharing lets tests that are not about visibility share freely between their users.
+func openSharing(t *testing.T, store *Store) {
+	t.Helper()
+	if store == nil {
+		return
+	}
+	sys, err := store.GetSystemSettings()
+	if err != nil {
+		t.Fatalf("GetSystemSettings: %v", err)
+	}
+	sys.SharingMode = SharingOpen
+	if err := store.UpdateSystemSettings(sys); err != nil {
+		t.Fatalf("UpdateSystemSettings: %v", err)
+	}
+}