feat(semantics): add semantic labels for UI automation

- Created lib/core/semantics/ with semantic ID constants and helper widget
- Enabled SemanticsBinding on web builds for accessibility tree exposure
- Added semantic IDs to:
  - ProfileDropdown (button, settings, theme options, logout)
  - TopHeaderBar room tabs (frontHall, controlRoom, security, parlor)
  - NavPanel items (nav_item_{id})

This enables browser automation tools like Puppeteer and WebDriver to
discover and interact with Flutter widgets via the accessibility tree.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

lib/core/semantics/semantic_ids.dart

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+/// Semantic identifiers for UI automation and accessibility.
+///
+/// These IDs are exposed via Flutter's Semantics tree, making widgets
+/// discoverable by automation tools (Appium, WebDriver, Puppeteer with
+/// accessibility enabled).
+///
+/// Naming convention: `{area}_{component}_{identifier}`
+/// - area: room or feature area (e.g., profile, nav, dataGrid)
+/// - component: widget type (e.g., menu, button, row)
+/// - identifier: specific item (e.g., light, containers, selectAll)
+library;
+
+/// Profile dropdown menu IDs.
+abstract class ProfileSemantics {
+  static const button = 'profile_button';
+  static const menu = 'profile_menu';
+  static const settings = 'profile_menu_settings';
+  static const themeSystem = 'profile_menu_theme_system';
+  static const themeLight = 'profile_menu_theme_light';
+  static const themeDark = 'profile_menu_theme_dark';
+  static const logout = 'profile_menu_logout';
+}
+
+/// Room tab navigation IDs.
+abstract class RoomTabSemantics {
+  static const frontHall = 'roomTab_frontHall';
+  static const controlRoom = 'roomTab_controlRoom';
+  static const security = 'roomTab_security';
+  static const parlor = 'roomTab_parlor';
+
+  /// Get semantic ID for room index.
+  static String forIndex(int index) => switch (index) {
+        0 => frontHall,
+        1 => controlRoom,
+        2 => security,
+        3 => parlor,
+        _ => 'roomTab_$index',
+      };
+}
+
+/// Navigation panel IDs.
+abstract class NavSemantics {
+  static const panel = 'nav_panel';
+  static const refresh = 'nav_refresh';
+
+  /// Generate ID for a nav item.
+  static String item(String id) => 'nav_item_$id';
+
+  /// Generate ID for a nav section.
+  static String section(String id) => 'nav_section_$id';
+}
+
+/// DataGrid component IDs.
+abstract class DataGridSemantics {
+  static const grid = 'dataGrid';
+  static const search = 'dataGrid_search';
+  static const searchClear = 'dataGrid_search_clear';
+  static const selectAll = 'dataGrid_selectAll';
+  static const loading = 'dataGrid_loading';
+  static const empty = 'dataGrid_empty';
+  static const error = 'dataGrid_error';
+  static const refresh = 'dataGrid_refresh';
+
+  /// Generate ID for a column header.
+  static String header(String columnId) => 'dataGrid_header_$columnId';
+
+  /// Generate ID for a row.
+  static String row(String itemId) => 'dataGrid_row_$itemId';
+
+  /// Generate ID for a row checkbox.
+  static String rowCheckbox(String itemId) => 'dataGrid_row_${itemId}_checkbox';
+
+  /// Generate ID for a row actions menu.
+  static String rowActions(String itemId) => 'dataGrid_row_${itemId}_actions';
+
+  /// Generate ID for a row action.
+  static String rowAction(String itemId, String actionId) =>
+      'dataGrid_row_${itemId}_action_$actionId';
+
+  /// Generate ID for a bulk action button.
+  static String bulkAction(String actionId) => 'dataGrid_bulk_$actionId';
+
+  static const bulkClear = 'dataGrid_bulk_clear';
+}
+
+/// Dialog/modal IDs.
+abstract class DialogSemantics {
+  static const confirm = 'dialog_confirm';
+  static const cancel = 'dialog_cancel';
+  static const close = 'dialog_close';
+
+  /// Generate ID for a named dialog.
+  static String named(String name) => 'dialog_$name';
+
+  /// Generate ID for a dialog action button.
+  static String action(String dialogName, String actionId) =>
+      'dialog_${dialogName}_$actionId';
+}
+
+/// Settings page IDs.
+abstract class SettingsSemantics {
+  static const themeDropdown = 'settings_theme';
+  static const defaultRoomDropdown = 'settings_defaultRoom';
+}
+
+/// Loading/state indicator IDs.
+abstract class StateSemantics {
+  static const authLoading = 'state_auth_loading';
+  static const authError = 'state_auth_error';
+  static const pageLoading = 'state_page_loading';
+
+  /// Generate ID for a snackbar.
+  static String snackbar(String type) => 'snackbar_$type';
+}

lib/core/semantics/semantic_widget.dart

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+import 'package:flutter/material.dart';
+
+/// Wraps a widget with semantic information for accessibility and automation.
+///
+/// Usage:
+/// ```dart
+/// SemanticWidget(
+///   id: ProfileSemantics.button,
+///   label: 'Open profile menu',
+///   child: IconButton(...),
+/// )
+/// ```
+///
+/// For buttons, use `button: true`. For other interactive elements,
+/// set the appropriate semantic properties.
+class SemanticWidget extends StatelessWidget {
+  const SemanticWidget({
+    super.key,
+    required this.id,
+    required this.child,
+    this.label,
+    this.hint,
+    this.button = false,
+    this.link = false,
+    this.header = false,
+    this.textField = false,
+    this.enabled = true,
+    this.selected,
+    this.checked,
+    this.value,
+    this.excludeSemantics = false,
+  });
+
+  /// Unique identifier for this widget, exposed via [SemanticsProperties.identifier].
+  final String id;
+
+  /// The widget to wrap.
+  final Widget child;
+
+  /// Accessibility label describing the widget.
+  final String? label;
+
+  /// Hint text for screen readers.
+  final String? hint;
+
+  /// Whether this widget represents a button.
+  final bool button;
+
+  /// Whether this widget represents a link.
+  final bool link;
+
+  /// Whether this widget represents a header.
+  final bool header;
+
+  /// Whether this widget represents a text field.
+  final bool textField;
+
+  /// Whether the widget is enabled.
+  final bool enabled;
+
+  /// Whether the widget is selected (for toggle buttons, tabs).
+  final bool? selected;
+
+  /// Whether the widget is checked (for checkboxes).
+  final bool? checked;
+
+  /// Current value (for sliders, progress indicators).
+  final String? value;
+
+  /// Whether to exclude child semantics.
+  final bool excludeSemantics;
+
+  @override
+  Widget build(BuildContext context) {
+    return Semantics(
+      identifier: id,
+      label: label,
+      hint: hint,
+      button: button,
+      link: link,
+      header: header,
+      textField: textField,
+      enabled: enabled,
+      selected: selected,
+      checked: checked,
+      value: value,
+      excludeSemantics: excludeSemantics,
+      child: child,
+    );
+  }
+}
+
+/// Extension to easily wrap any widget with semantic info.
+extension SemanticExtension on Widget {
+  /// Wraps this widget with a semantic identifier.
+  Widget withSemantics({
+    required String id,
+    String? label,
+    String? hint,
+    bool button = false,
+    bool link = false,
+    bool enabled = true,
+    bool? selected,
+    bool? checked,
+  }) {
+    return SemanticWidget(
+      id: id,
+      label: label,
+      hint: hint,
+      button: button,
+      link: link,
+      enabled: enabled,
+      selected: selected,
+      checked: checked,
+      child: this,
+    );
+  }
+}