refactor(chat): split ChatScreen and reuse regenerateResponse after editing a message

The edit path duplicated the streaming flow with inline require() calls; it now reuses regenerateResponse, which also fixes:
- edited conversations were never saved to History
- the answer generated after an edit could not be stopped (no abort handle kept)
Stopping a stream now saves the partial conversation, like finishing or failing does.
Adds characterization tests for ChatScreen and useLMStudio.

components/chat/EmptyState.tsx

@@ -0,0 +1,99 @@
+import { useThemeColor } from '@/hooks/useThemeColor';
+import { MessageSquare, Sparkles } from 'lucide-react-native';
+import React from 'react';
+import { StyleSheet, Text, TouchableOpacity, View } from 'react-native';
+
+export const PROMPT_SUGGESTIONS = [
+    'Explain recursion in simple terms',
+    'Write a short poem about coding',
+    'What are the best practices for React Native?',
+    'Help me debug a JavaScript error',
+];
+
+interface EmptyStateProps {
+    onSelectPrompt: (prompt: string) => void;
+}
+
+export function EmptyState({ onSelectPrompt }: EmptyStateProps) {
+    const colors = useThemeColor();
+
+    return (
+        <View style={[styles.emptyState, { backgroundColor: colors.backgroundColor }]}>
+            <View style={[styles.emptyIconWrap, { backgroundColor: colors.cardBackground, shadowColor: colors.shadow }]}>
+                <MessageSquare size={40} color={colors.textMuted} />
+            </View>
+            <Text style={[styles.emptyTitle, { color: colors.text }]}>Start a conversation</Text>
+            <Text style={[styles.emptySubtitle, { color: colors.textMuted }]}>
+                Send a message to begin chatting with your local AI model.
+            </Text>
+
+            <View style={styles.suggestionsWrap}>
+                {PROMPT_SUGGESTIONS.map((prompt) => (
+                    <TouchableOpacity
+                        key={prompt}
+                        style={[styles.suggestionChip, { backgroundColor: colors.cardBackground, borderColor: colors.border }]}
+                        onPress={() => onSelectPrompt(prompt)}
+                        activeOpacity={0.7}
+                        accessibilityRole="button"
+                        accessibilityLabel={prompt}
+                    >
+                        <Sparkles size={14} color={colors.textMuted} />
+                        <Text style={[styles.suggestionText, { color: colors.text }]} numberOfLines={1}>{prompt}</Text>
+                    </TouchableOpacity>
+                ))}
+            </View>
+        </View>
+    );
+}
+
+const styles = StyleSheet.create({
+    emptyState: {
+        flex: 1,
+        alignItems: 'center',
+        justifyContent: 'center',
+        paddingHorizontal: 32,
+        paddingBottom: 80,
+    },
+    emptyIconWrap: {
+        width: 80,
+        height: 80,
+        borderRadius: 40,
+        alignItems: 'center',
+        justifyContent: 'center',
+        marginBottom: 20,
+        shadowOffset: { width: 0, height: 4 },
+        shadowOpacity: 0.05,
+        shadowRadius: 10,
+        elevation: 2,
+    },
+    emptyTitle: {
+        fontSize: 22,
+        fontWeight: '700',
+        marginBottom: 8,
+    },
+    emptySubtitle: {
+        fontSize: 15,
+        textAlign: 'center',
+        lineHeight: 22,
+        marginBottom: 32,
+    },
+    suggestionsWrap: {
+        width: '100%',
+        maxWidth: 400,
+        gap: 12,
+    },
+    suggestionChip: {
+        flexDirection: 'row',
+        alignItems: 'center',
+        gap: 12,
+        borderWidth: 1,
+        borderRadius: 16,
+        paddingHorizontal: 16,
+        paddingVertical: 14,
+    },
+    suggestionText: {
+        fontSize: 15,
+        flex: 1,
+        fontWeight: '500',
+    },
+});