feat: Large File Support — proxy, operator, SDKs, and demos

[kamir]

Summary

Complete LFS (Large File Support) subsystem for streaming large binary payloads through KafScale via S3-backed object storage with Kafka metadata references.

Core LFS Proxy (119 files)

• LFS proxy server (cmd/lfs-proxy/) — HTTP upload/download, S3 backend, Kafka record publishing, Prometheus metrics, checksum verification, TLS/SASL support, OpenAPI spec
• LFS package (pkg/lfs/) — shared types, producer, consumer, resolver, envelope, and S3 client logic
• Operator integration — reconcile LFS proxy Deployment, Service, and ConfigMap as part of KafscaleCluster CR
• Console LFS admin (internal/console/) — object/topic/orphan browsing handlers
• IDoc exploder (cmd/idoc-explode/) — SAP IDoc payload processing with field aggregation into routed parent segments
• Iceberg processor — LFS-aware decoding and config extensions
• Helm charts — LFS proxy deployment, metrics, monitoring, and ServiceMonitor templates
• E2E tests — LFS proxy broker, HTTP, etcd, SDK, and iceberg processor tests
• CI pipeline — Docker build for LFS proxy image, stage-release workflow
• Documentation — architecture, data-flow, security hardening, Helm deployment, SDK roadmap

Client SDKs & Demos (97 files)

• Java SDK — retry/backoff, configurable timeouts, Maven build
• Python SDK — retry/backoff, envelope codec, pip-installable
• JavaScript SDK (Node.js) — streaming upload support
• Browser SDK (JS) — SPA-based LFS file management
• Demos — E60-E62 (industry designs), E70 (Java), E71 (Python), E72 (browser SPA)
• Docker Compose stack for local LFS development

Fixes included

• Fix missing time import in lfs_handlers.go
• Fix Makefile script name mismatches (lfs-demo-medical.sh → medical-lfs-demo.sh)
• Add missing LFS demo scripts not included in initial branch split
• Fix wrong LFS envelope field names in demo scripts (lfs_version → kfs_lfs)
• Enrich IDoc exploder with Fields map for parent segment field aggregation
• Enrich IDoc demo with full LFS pipeline (S3 upload → envelope → resolve → explode)
• Add Apache 2.0 license headers to 12 files
• Fix S3 blob verification in medical/video/industrial demos (*.meta → obj-*)

Test plan

• go vet ./... passes
• go test -race ./... passes
• go build ./cmd/lfs-proxy passes
• License header check passes (hack/check_license_headers.py)
• Helm lint passes (helm lint deploy/helm/kafscale)
• Coverage gate passes (80% floor)
• E2E tests with MinIO + broker (requires cluster infrastructure)
• Helm chart deployment validation on kind cluster

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