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_widget.dart

@@ -0,0 +1,118 @@
+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,
+    );
+  }
+}