feat: close STREAMING.md production readiness gaps

- Added run ID + unique segment naming (r-{ISOTIME}/seg-{seq}.m4s)
- Added fsnotify watcher for real-time R2 segment upload (~7s)
- Added atomic manifest publication (temp key → CopyObject)
- Fixed manifest Cache-Control: public, max-age=1, s-maxage=2, must-revalidate
- Added hls.js error recovery: bounded retries (5x), exponential backoff, reconnecting UI
- Enriched /health endpoint: run_id, active_item, last_segment_seq, last_r2_pub, consecutive_failures, unhealthy detection
- Updated tests: HealthHandler (new fields + unhealthy), player error recovery test
- Updated TODO.md, BACKLOG.md, DONE.md, MEMORY.md

backend/playout/src/go.mod

@@ -6,6 +6,7 @@ require (
 	github.com/aws/aws-sdk-go-v2 v1.43.4
 	github.com/aws/aws-sdk-go-v2/config v1.32.35
 	github.com/aws/aws-sdk-go-v2/service/s3 v1.107.0
+	github.com/fsnotify/fsnotify v1.8.0
 )
 
 require (
@@ -24,4 +25,5 @@ require (
 	github.com/aws/aws-sdk-go-v2/service/ssooidc v1.38.4 // indirect
 	github.com/aws/aws-sdk-go-v2/service/sts v1.45.4 // indirect
 	github.com/aws/smithy-go v1.27.6 // indirect
+	golang.org/x/sys v0.13.0 // indirect
 )