refactor(database): migrate to new modular database layer and unify data access

- Remove legacy database.ts, LocalDataSource.ts, and MessageRepository.ts
- Create new src/database/ module with messageRepository, userCacheRepository, conversationRepository, and groupCacheRepository
- Update all consumers to import from @/database instead of services/database
- Add web platform blur handling for modal components to fix focus issues
- Flatten SystemMessageItem and NotificationsScreen styles for consistent design
- Add draggable slider in ChatSettingsScreen and dynamic font size support
- Introduce 9 new chat color themes
- Add profile screens for about, terms, and privacy policy with navigation routes
- Add policy links to login and registration screens
- Fix post share URL format from /posts/ to /post/

src/screens/auth/LoginScreen.tsx

@@ -237,6 +237,16 @@ export const LoginScreen: React.FC = () => {
                 <Text style={styles.registerLink}>立即注册</Text>
               </TouchableOpacity>
             </View>
+
+            {/* 协议提示 */}
+            <View style={styles.policyFooter}>
+              <Text style={styles.policyText}>
+                登录即表示您同意
+                <Text style={styles.policyLink} onPress={() => router.push(hrefs.hrefProfileTerms())}>《用户协议》</Text>
+                和
+                <Text style={styles.policyLink} onPress={() => router.push(hrefs.hrefProfilePrivacy())}>《隐私政策》</Text>
+              </Text>
+            </View>
           </Animated.View>
         </ScrollView>
       </KeyboardAvoidingView>
@@ -376,6 +386,18 @@ function createLoginStyles(colors: AppColors) {
       fontWeight: '600',
       marginLeft: 6,
     },
+    policyFooter: {
+      alignItems: 'center',
+      marginTop: 24,
+    },
+    policyText: {
+      fontSize: 13,
+      color: colors.text.hint,
+    },
+    policyLink: {
+      color: THEME_COLORS.primary,
+      fontWeight: '500',
+    },
   });
 }
 

src/screens/auth/RegisterStep3Profile.tsx

@@ -12,9 +12,11 @@ import {
   TouchableOpacity,
   ActivityIndicator,
 } from 'react-native';
+import { useRouter } from 'expo-router';
 import { MaterialCommunityIcons } from '@expo/vector-icons';
 import { useAppColors, type AppColors } from '../../theme';
 import { RegisterStepProps } from './types';
+import * as hrefs from '../../navigation/hrefs';
 
 const THEME_COLORS = {
   primary: '#FF6B35',
@@ -32,6 +34,7 @@ export const RegisterStep3Profile: React.FC<RegisterStepProps> = ({
 }) => {
   const colors = propColors || useAppColors();
   const styles = createStyles(colors);
+  const router = useRouter();
 
   const [showPassword, setShowPassword] = useState(false);
   const [showConfirmPassword, setShowConfirmPassword] = useState(false);
@@ -185,28 +188,40 @@ export const RegisterStep3Profile: React.FC<RegisterStepProps> = ({
         })}
 
         {/* 服务条款 */}
-        <TouchableOpacity
-          style={styles.termsContainer}
-          onPress={() => {
-            setAgreedToTerms(!agreedToTerms);
-            if (errors.terms) {
-              setErrors((prev) => ({ ...prev, terms: '' }));
-            }
-          }}
-          activeOpacity={0.8}
-        >
-          <MaterialCommunityIcons
-            name={agreedToTerms ? 'checkbox-marked' : 'checkbox-blank-outline'}
-            size={22}
-            color={agreedToTerms ? THEME_COLORS.primary : colors.text?.hint || '#999'}
-          />
+        <View style={styles.termsContainer}>
+          <TouchableOpacity
+            onPress={() => {
+              setAgreedToTerms(!agreedToTerms);
+              if (errors.terms) {
+                setErrors((prev) => ({ ...prev, terms: '' }));
+              }
+            }}
+            activeOpacity={0.8}
+            style={styles.checkboxWrapper}
+          >
+            <MaterialCommunityIcons
+              name={agreedToTerms ? 'checkbox-marked' : 'checkbox-blank-outline'}
+              size={22}
+              color={agreedToTerms ? THEME_COLORS.primary : colors.text?.hint || '#999'}
+            />
+          </TouchableOpacity>
           <Text style={styles.termsText}>
             我已阅读并同意
-            <Text style={styles.termsLink}>《用户协议》</Text>
+            <Text
+              style={styles.termsLink}
+              onPress={() => router.push(hrefs.hrefProfileTerms())}
+            >
+              《用户协议》
+            </Text>
             和
-            <Text style={styles.termsLink}>《隐私政策》</Text>
+            <Text
+              style={styles.termsLink}
+              onPress={() => router.push(hrefs.hrefProfilePrivacy())}
+            >
+              《隐私政策》
+            </Text>
           </Text>
-        </TouchableOpacity>
+        </View>
         {errors.terms ? (
           <Text style={[styles.errorText, { marginTop: -12, marginBottom: 12 }]}>
             {errors.terms}
@@ -295,10 +310,13 @@ function createStyles(colors: AppColors) {
     },
     termsContainer: {
       flexDirection: 'row',
-      alignItems: 'center',
+      alignItems: 'flex-start',
       marginBottom: 20,
       marginTop: 4,
     },
+    checkboxWrapper: {
+      paddingTop: 2,
+    },
     termsText: {
       fontSize: 14,
       color: colors.text?.secondary || '#666',