Fix tech hotspot GitHub auth and rate-limit handling

[lisihao]

摘要

• 给 Tech Hotspot Radar 补 GitHub token 发现与 typed rate-limit / API error 语义
• 让 GitHub metadata enrichment 在默认情况下优先走本地 repo 表，只有显式开启时才打 live API
• 调整 materialize / collect 流程对 rate limit 的处理，并给 run script 补 gh auth token 回退

变更边界

in-scope

• harness/config/tech-hotspot-radar.yaml
• harness/scripts/run_tech_hotspot_radar.sh
• harness/scripts/tech_hotspot_radar.py
• harness/tests/test_github_api_auth_rate_limit.py

out-of-scope

• 不改 runtime drift sticky / graph projection 主链
• 不改 dispatch reconcile / pm_dispatch closeout 守卫
• 不处理原工作区其他并行 feature 脏改动

已验证

• python3 -m pytest -q harness/tests/test_github_api_auth_rate_limit.py harness/tests/test_tech_hotspot_browser_agent_cmd.py
  • 24 passed
• bash -n harness/scripts/run_tech_hotspot_radar.sh
  • 通过
• python3 -m py_compile harness/scripts/tech_hotspot_radar.py
  • 通过

堆叠关系

• base: codex/runtime-drift-writepath-fix
• 与 dispatch_pool / operator_view_status / browser_operator / pm_router 为并列后续分支，不互相依赖