feat(a11y): label icon-only buttons and inputs for screen readers

Header, message action, send/stop, history, model selector and dark-mode controls had no accessible name (icon-only buttons). Adds roles/labels and selected/disabled state; no visual change.

components/chat/ChatInput.tsx

@@ -65,7 +65,12 @@ export function ChatInput({ onSend, onStop, isLoading, editingText, onCancelEdit
             {isEditing && (
                 <View style={[styles.editBanner, { backgroundColor: colors.bannerBg, borderBottomColor: colors.border }]}>
                     <Text style={[styles.editBannerText, { color: colors.bannerText }]}>Editing message</Text>
-                    <TouchableOpacity onPress={handleCancelEdit} style={styles.editCancelBtn}>
+                    <TouchableOpacity
+                        onPress={handleCancelEdit}
+                        style={styles.editCancelBtn}
+                        accessibilityRole="button"
+                        accessibilityLabel="Cancel editing"
+                    >
                         <X size={16} color={colors.textMuted} />
                     </TouchableOpacity>
                 </View>
@@ -80,6 +85,7 @@ export function ChatInput({ onSend, onStop, isLoading, editingText, onCancelEdit
                     <TextInput
                         style={[styles.input, { color: colors.text }]}
                         placeholder="Send a message..."
+                        accessibilityLabel="Message"
                         placeholderTextColor={colors.textMuted}
                         value={text}
                         onChangeText={setText}
@@ -94,6 +100,8 @@ export function ChatInput({ onSend, onStop, isLoading, editingText, onCancelEdit
                             style={[styles.stopButton, { backgroundColor: colors.errorText }]}
                             onPress={handleStop}
                             activeOpacity={0.7}
+                            accessibilityRole="button"
+                            accessibilityLabel="Stop generating"
                         >
                             <Square size={16} color={colors.backgroundColor} />
                         </TouchableOpacity>
@@ -106,6 +114,9 @@ export function ChatInput({ onSend, onStop, isLoading, editingText, onCancelEdit
                             onPress={handleSend}
                             disabled={!text.trim()}
                             activeOpacity={0.7}
+                            accessibilityRole="button"
+                            accessibilityLabel="Send message"
+                            accessibilityState={{ disabled: !text.trim() }}
                         >
                             <Send size={18} color={text.trim() ? colors.backgroundColor : colors.textMuted} />
                         </TouchableOpacity>