refactor(provider): use local settings for current provider selection

Complete the device-level settings separation for cloud sync support.

Backend changes:
- Modify switch() to update both local settings and database is_current
- Modify current() to read from local settings first, fallback to database
- Rename sync_current_from_db() to sync_current_to_live()
- Update tray menu to read current provider from local settings

Frontend changes:
- Update Settings interface: remove legacy fields (customEndpoints*, security)
- Add currentProviderClaude/Codex/Gemini fields
- Update settings schema accordingly

Test fixes:
- Update Gemini security tests to check ~/.gemini/settings.json
  instead of ~/.cc-switch/settings.json (security field was never
  stored in CC Switch settings)

This ensures each device maintains its own current provider selection
independently when database is synced across devices.

src/lib/schemas/settings.ts

@@ -8,14 +8,22 @@ const directorySchema = z
   .or(z.literal(""));
 
 export const settingsSchema = z.object({
+  // 设备级 UI 设置
   showInTray: z.boolean(),
   minimizeToTrayOnClose: z.boolean(),
   enableClaudePluginIntegration: z.boolean().optional(),
+  launchOnStartup: z.boolean().optional(),
+  language: z.enum(["en", "zh"]).optional(),
+
+  // 设备级目录覆盖
   claudeConfigDir: directorySchema.nullable().optional(),
   codexConfigDir: directorySchema.nullable().optional(),
-  language: z.enum(["en", "zh"]).optional(),
-  customEndpointsClaude: z.record(z.string(), z.unknown()).optional(),
-  customEndpointsCodex: z.record(z.string(), z.unknown()).optional(),
+  geminiConfigDir: directorySchema.nullable().optional(),
+
+  // 当前供应商 ID（设备级）
+  currentProviderClaude: z.string().optional(),
+  currentProviderCodex: z.string().optional(),
+  currentProviderGemini: z.string().optional(),
 });
 
 export type SettingsFormData = z.infer<typeof settingsSchema>;