feat: add session log usage tracking without proxy

Parse Claude Code JSONL session files (~/.claude/projects/) and Codex
SQLite database (~/.codex/state_5.sqlite) to track API usage without
requiring proxy interception. This enables usage statistics for users
who don't use the proxy feature.

Key changes:
- Add session_usage.rs: incremental JSONL parser with message.id dedup
- Add session_usage_codex.rs: import thread-level token data from Codex
- Add data_source column to proxy_request_logs (proxy/session_log/codex_db)
- Add session_log_sync table for tracking parse offsets
- Background sync every 60s + manual sync via DataSourceBar UI
- Schema migration v7→v8
- i18n support for zh/en/ja

src/types/usage.ts

@@ -31,6 +31,20 @@ export interface RequestLog {
   statusCode: number;
   errorMessage?: string;
   createdAt: number;
+  dataSource?: string;
+}
+
+export interface SessionSyncResult {
+  imported: number;
+  skipped: number;
+  filesScanned: number;
+  errors: string[];
+}
+
+export interface DataSourceSummary {
+  dataSource: string;
+  requestCount: number;
+  totalCostUsd: string;
 }
 
 export interface PaginatedLogs {