docs(spec): add PR #16 blocking issues analysis

Comprehensive analysis of 4 blocking issues from PR #16 code reviews:

Issue Status:
✅ #1: Proto breaking changes (resolved 2025-11-27)
✅ #2: Lint errors (203 violations, resolved 2025-11-27)
⚠️ #3: PR scope too large (365 files, CRITICAL BLOCKER)
✅ #4: json.dumpb() AttributeError (resolved 2025-12-11)

Remaining Blocker:
- PR scope: 365 files (70 support files + 295 code files)
- Required: Reduce to < 50 files, focus on Kafka backend only
- Action: Remove .claude/*, .kiro/* (except kafka spec), .env templates
- Timeline: 1-2 hours manual work

Document includes:
- Detailed root cause analysis for each issue
- Resolution verification for resolved issues
- 3 recommended options for scope reduction
- Success criteria and timeline estimates

Spec: kafka-protobuf-binance-e2e
PR: #16 (feature/kafka-proto-backend → next)

Author: tommy-ca