feat(account): danger zone, restore import, larger API key field on phones

- Danger zone in settings: delete all own data or the account, both with
  password confirmation; the last server admin cannot delete the account
- DELETE /user/data and /user/account; PurgeUserData removes everything a
  user owns in one transaction (others' tasks in shared lists stay theirs),
  also used by admin user deletion
- MindSift import: 'Hinzufügen' or 'Wiederherstellen' (mode=restore, wipes
  own data only after the file is fully validated, confirm checkbox)
- API key name field and button 44 px on phones (flex-1 collapsed them)

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

internal/storage/account.go

@@ -0,0 +1,92 @@
+package storage
+
+import (
+	"errors"
+	"fmt"
+)
+
+// ErrLastAdmin protects the server from losing its last administrator.
+var ErrLastAdmin = errors.New("Der letzte Server-Administrator kann nicht gelöscht werden. Bitte ernenne vorher ein anderes Konto zum Administrator.")
+
+// PurgeUserData deletes everything the user owns – thoughts and tasks, notes (with blocks, history and
+// shares), folders, shared folders, task lists and lists – in one transaction. The account, its
+// settings, themes, API keys and group memberships stay. Other people's tasks in the user's task lists
+// become their own personal tasks, as when a single list is deleted.
+func (s *Store) PurgeUserData(userID string) error {
+	tx, err := s.db.Begin()
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback()
+
+	ownDocs := `(SELECT id FROM documents WHERE user_id = ?)`
+	ownTaskLists := `(SELECT id FROM task_lists WHERE user_id = ?)`
+	ownFolders := `(SELECT id FROM workspace_shared_folders WHERE owner_id = ?)`
+	stmts := []struct {
+		q    string
+		args int // how many times userID is passed
+	}{
+		// Task lists: keep the tasks of others, drop shares and the lists
+		{`UPDATE thoughts SET task_list_id = '' WHERE task_list_id IN ` + ownTaskLists + ` AND user_id != ?`, 2},
+		{`DELETE FROM task_list_shares WHERE task_list_id IN ` + ownTaskLists, 1},
+		{`DELETE FROM task_lists WHERE user_id = ?`, 1},
+		// Tasks of others linked to blocks of the user's notes lose the link
+		{`UPDATE thoughts SET converted_type = '', converted_ref_id = '' WHERE converted_type = 'document_block'
+		  AND substr(converted_ref_id, 1, instr(converted_ref_id, ':') - 1) IN ` + ownDocs, 1},
+		{`DELETE FROM thoughts WHERE user_id = ?`, 1},
+		// Shared folders owned by the user
+		{`UPDATE documents SET shared_folder_id = '', sub_folder_path = '' WHERE shared_folder_id IN ` + ownFolders, 1},
+		{`DELETE FROM workspace_folder_mounts WHERE folder_id IN ` + ownFolders, 1},
+		{`DELETE FROM workspace_folder_shares WHERE folder_id IN ` + ownFolders, 1},
+		{`DELETE FROM workspace_folders WHERE shared_folder_id IN ` + ownFolders, 1},
+		{`DELETE FROM workspace_shared_folders WHERE owner_id = ?`, 1},
+		// Notes (history tables cascade with the document)
+		{`DELETE FROM blocks WHERE document_id IN ` + ownDocs, 1},
+		{`DELETE FROM block_tags WHERE document_id IN ` + ownDocs, 1},
+		{`DELETE FROM doc_user_folders WHERE doc_id IN ` + ownDocs, 1},
+		{`DELETE FROM doc_team_shares WHERE doc_id IN ` + ownDocs, 1},
+		{`DELETE FROM doc_shares WHERE doc_id IN ` + ownDocs, 1},
+		{`DELETE FROM documents WHERE user_id = ?`, 1},
+		// The user's own placement of notes, folders, pins and tag pages
+		{`DELETE FROM doc_user_folders WHERE user_id = ?`, 1},
+		{`DELETE FROM doc_pins WHERE user_id = ?`, 1},
+		{`DELETE FROM workspace_folders WHERE user_id = ?`, 1},
+		{`DELETE FROM tag_pages WHERE user_id = ?`, 1},
+		// Lists (items cascade)
+		{`DELETE FROM list_shares WHERE list_id IN (SELECT id FROM lists WHERE user_id = ?)`, 1},
+		{`DELETE FROM lists WHERE user_id = ?`, 1},
+	}
+	for _, st := range stmts {
+		args := make([]interface{}, st.args)
+		for i := range args {
+			args[i] = userID
+		}
+		if _, err := tx.Exec(st.q, args...); err != nil {
+			return fmt.Errorf("Daten löschen: %w", err)
+		}
+	}
+	if err := tx.Commit(); err != nil {
+		return err
+	}
+	s.PruneTaskAssignees()
+	return nil
+}
+
+// IsLastAdmin reports whether userID is an administrator and no other one exists.
+func (s *Store) IsLastAdmin(userID string) bool {
+	var role string
+	if err := s.db.QueryRow(`SELECT role FROM users WHERE id = ?`, userID).Scan(&role); err != nil || role != "admin" {
+		return false
+	}
+	var others int
+	_ = s.db.QueryRow(`SELECT COUNT(*) FROM users WHERE role = 'admin' AND id != ?`, userID).Scan(&others)
+	return others == 0
+}
+
+// DeleteOwnAccount removes the user with all data; refused for the last administrator.
+func (s *Store) DeleteOwnAccount(userID string) error {
+	if s.IsLastAdmin(userID) {
+		return ErrLastAdmin
+	}
+	return s.DeleteUser(userID)
+}