feat: add privacy mode, thinking levels, PWA support, and i18n

- Add privacy mode to hide IP and user preferences from AI requests
- Add model thinking levels (low/medium/high) for context analysis depth
- Add PWA support with service worker, manifest, and app icons
- Add SettingsPanel for user preferences (theme, background, language)
- Add i18n translations for en/zh/ja/ko/de/fr
- Add Pinia store for centralized settings management
- Update backend to support user preferences and thinking levels
- Update config to use absolute API URLs

src/stores/settings.js

@@ -0,0 +1,156 @@
+import { defineStore } from 'pinia'
+import { ref, watch, computed } from 'vue'
+import { translations } from '../utils/i18n'
+
+export const useSettingsStore = defineStore('settings', () => {
+    // --- State ---
+
+    // 1. Theme (handled partly by useTheme, but we keep a ref here for the UI)
+    const theme = ref('system') // 'light' | 'dark' | 'system'
+
+    // 2. Model Behavior
+    const modelThinking = ref('low') // 'low' | 'medium' | 'high'
+    const debounceMs = ref(1000) // 1000 - 5000
+
+    // 3. Privacy
+    const privacyMode = ref(false)
+
+    // 4. Preferences
+    const language = ref('auto')
+    const currency = ref('auto')
+    // const timezone = ref('auto') // removed
+
+    // 5. Background
+    const backgroundType = ref('default') // 'default' | 'warm' | 'reading' | 'image'
+    // const backgroundColor = ref('#ffffff') // removed
+    const backgroundImage = ref('')
+    const backgroundOpacity = ref(0.2) // 0.05 - 0.50
+
+    // --- Getters ---
+    const uiLanguage = computed(() => {
+        if (language.value !== 'auto') {
+            return language.value
+        }
+        const sysLang = (navigator.language || navigator.userLanguage || 'en').split('-')[0]
+        const supported = ['zh', 'en', 'ja', 'ko', 'de', 'fr']
+        return supported.includes(sysLang) ? sysLang : 'en'
+    })
+
+    const detectedTimezone = computed(() => {
+        return Intl.DateTimeFormat().resolvedOptions().timeZone || 'UTC'
+    })
+
+    // We can't easily detect currency by IP on the frontend without an external API.
+    // We will let the backend handle 'auto' currency if needed, or stick to auto label.
+
+    const t = computed(() => {
+        return translations[uiLanguage.value] || translations['en']
+    })
+
+    // --- Actions/Logic ---
+
+    // Load from localStorage
+    const loadSettings = () => {
+        try {
+            const stored = localStorage.getItem('llm-in-text-settings')
+            if (stored) {
+                const data = JSON.parse(stored)
+                if (data.theme) theme.value = data.theme
+                if (data.modelThinking) modelThinking.value = data.modelThinking
+                if (data.debounceMs) debounceMs.value = data.debounceMs
+                if (typeof data.privacyMode === 'boolean') privacyMode.value = data.privacyMode
+                if (data.language) language.value = data.language
+                if (data.currency) currency.value = data.currency
+                // if (data.timezone) timezone.value = data.timezone // timezone legacy ignore
+                if (data.backgroundType) {
+                    // migrate color to default if needed, or mapped
+                    if (data.backgroundType === 'color') backgroundType.value = 'default'
+                    else backgroundType.value = data.backgroundType
+                }
+                // if (data.backgroundColor) backgroundColor.value = data.backgroundColor // removed
+                if (data.backgroundImage) backgroundImage.value = data.backgroundImage
+                if (data.backgroundOpacity) backgroundOpacity.value = data.backgroundOpacity
+            }
+        } catch (e) {
+            console.error('Failed to load settings', e)
+        }
+    }
+
+    // Save to localStorage
+    const saveSettings = () => {
+        try {
+            const data = {
+                theme: theme.value,
+                modelThinking: modelThinking.value,
+                debounceMs: debounceMs.value,
+                privacyMode: privacyMode.value,
+                language: language.value,
+                currency: currency.value,
+                // timezone: timezone.value, // removed
+                backgroundType: backgroundType.value,
+                // backgroundColor: backgroundColor.value, // removed
+                backgroundImage: backgroundImage.value,
+                backgroundOpacity: backgroundOpacity.value,
+            }
+            localStorage.setItem('llm-in-text-settings', JSON.stringify(data))
+        } catch (e) {
+            console.error('Failed to save settings', e)
+        }
+    }
+
+    // Reset to defaults
+    const resetSettings = () => {
+        theme.value = 'system'
+        modelThinking.value = 'low'
+        debounceMs.value = 1000
+        privacyMode.value = false
+        language.value = 'auto'
+        currency.value = 'auto'
+        // timezone.value = 'auto' // removed
+        backgroundType.value = 'default'
+        // backgroundColor.value = '#ffffff' // removed
+        backgroundImage.value = ''
+        backgroundOpacity.value = 0.2
+        saveSettings()
+    }
+
+    // Auto-save watchers
+    watch(
+        [
+            theme,
+            modelThinking,
+            debounceMs,
+            privacyMode,
+            language,
+            currency,
+            // timezone, // removed
+            backgroundType,
+            // backgroundColor, // removed
+            backgroundImage,
+            backgroundOpacity,
+        ],
+        () => {
+            saveSettings()
+        }
+    )
+
+    // Initialize
+    loadSettings()
+
+    return {
+        theme,
+        modelThinking,
+        debounceMs,
+        privacyMode,
+        language,
+        currency,
+        // timezone, // removed
+        backgroundType,
+        // backgroundColor, // removed
+        backgroundImage,
+        backgroundOpacity,
+        uiLanguage,
+        t,
+        resetSettings
+    }
+})