feat: add Gemini CLI session log usage tracking

Parse ~/.gemini/tmp/*/chats/session-*.json for precise per-message
token data (input/output/cached/thoughts). Integrates with existing
background sync and manual sync button alongside Claude and Codex.

src/components/usage/DataSourceBar.tsx

@@ -16,6 +16,7 @@ const DATA_SOURCE_ICONS: Record<string, React.ReactNode> = {
   session_log: <FileText className="h-3.5 w-3.5" />,
   codex_db: <Database className="h-3.5 w-3.5" />,
   codex_session: <FileText className="h-3.5 w-3.5" />,
+  gemini_session: <FileText className="h-3.5 w-3.5" />,
 };
 
 export function DataSourceBar({ refreshIntervalMs }: DataSourceBarProps) {

src/i18n/locales/en.json

@@ -1024,7 +1024,8 @@
       "proxy": "Proxy",
       "session_log": "Session Log",
       "codex_db": "Codex DB",
-      "codex_session": "Codex Session"
+      "codex_session": "Codex Session",
+      "gemini_session": "Gemini Session"
     },
     "sessionSync": {
       "trigger": "Sync session logs",

src/i18n/locales/ja.json

@@ -1024,7 +1024,8 @@
       "proxy": "プロキシ",
       "session_log": "セッションログ",
       "codex_db": "Codex DB",
-      "codex_session": "Codex セッション"
+      "codex_session": "Codex セッション",
+      "gemini_session": "Gemini セッション"
     },
     "sessionSync": {
       "trigger": "セッションログを同期",

src/i18n/locales/zh.json

@@ -1024,7 +1024,8 @@
       "proxy": "代理",
       "session_log": "会话日志",
       "codex_db": "Codex 数据库",
-      "codex_session": "Codex 会话日志"
+      "codex_session": "Codex 会话日志",
+      "gemini_session": "Gemini 会话日志"
     },
     "sessionSync": {
       "trigger": "同步会话日志",