fix: 7-category audit sweep — daemon threads, file handles, stale data, L3 counts, dead files, dispatch, except:pass

- builder.py/mcp_server.py: SymversGuard + cleanup threads now log exceptions + retry instead of silent crash
- builder.py/error_classifier.py/benchmark_fetch_cves.py: 3 unclosed file handles → with-context
- test_rag.py: fix stale assertion to match current prompt template
- README/设计方案/project_progress/gitlab_design: L3 10→8 (06-09 ECS verified)
- agent.py/server.py: deleted dead compat files, imports migrated to agents.rewrite_agent
- coordinator_agent.py: _dispatch() now raises ValueError on unknown state instead of silent return
- rewrite_agent/knowledge_base/init_rag_db/mcp_server: 4 low-risk except:pass → logging.debug

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>