Limit OG image generation concurrency

[retlehs]

Summary

• Under heavy crawler traffic, unbounded go generatePackageOG() goroutines
  were constantly contesting the SQLite write lock, causing the pipeline to
  fail with SQLITE_BUSY
• Adds a non-blocking semaphore (capacity 2) — excess requests skip generation
  instead of queuing, so the image gets generated on the next page visit
• Combined with the busy_timeout increase (b71d4f5), this should eliminate
  pipeline failures from OG lock contention

Test plan

• make test passes
• Deploy and verify pipeline completes during heavy traffic
• Verify OG images still generate (just throttled)

🤖 Generated with Claude Code

[tangrufus]

Wrap handleDetail in a rate limiting middleware seems a better choice

[tangrufus]

Example: https://eli.thegreenplace.net/2019/on-concurrency-in-go-http-servers/#limiting-the-degree-of-concurrency-for-our-server

[retlehs]

Thank you, will take a peek tomorrow or sometime soon