refactor(goroutine): replace bare goroutines with managed executors
- Add internal/pkg/safego/ utility for safe goroutine launching
with panic recovery, structured logging (slog + zap), and optional
error callback support
- Replace 8 fire-and-forget goroutines in service layer:
user_service.go (1), subscription_service.go (4), redeem_service.go (2),
promo_service.go (1) — all now use safego.Go()
- Add inline panic recovery to 6 long-running goroutines:
pricing_service.go scheduler loop
Redis PubSub subscribers: tls_fingerprint/error_passthrough/api_key caches
OAuth session cleanup: openai/oauth/geminicli
S3 stream upload in sora_s3_storage.go
- All changes verified: go build PASS, service tests ALL PASS,
repository tests ALL PASS
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