docs: archive historical planning documents and fix references

Move self-described historical/upstream docs to docs/archive/:
- agent-runbook-guide.md
- lan-core-switch-upgrade-plan.md
- lan-rb5009-upgrade.md
- se5420-review-claim-verification-2026-08.md

Update archive/README.md manifest and fix relative links in active docs
and archived docs. Update AGENTS.md docs/ layout description.

docs/archive/README.md

@@ -8,6 +8,10 @@
 | 文件 | 归档日期 | 原位置 | 说明 |
 |------|---------|--------|------|
 | `lan-dns-alternatives.md` | 2026-08-17 | `docs/` | DNS 技术选型调研，零引用，无在途决策 |
+| `agent-runbook-guide.md` | 2026-08-22 | `docs/` | 上游参考存档；仓库落地规范为 `RUNBOOKS.md` |
+| `lan-core-switch-upgrade-plan.md` | 2026-08-22 | `docs/` | SE5420 历史规划参考；执行以 `docs/lan-se5420-deployment-guide.md` 为准 |
+| `lan-rb5009-upgrade.md` | 2026-08-22 | `docs/` | 未采购的 ER-X→RB5009 休眠备选方案；其中 PVE 透传与 VLAN10 调研仍可参考 |
+| `se5420-review-claim-verification-2026-08.md` | 2026-08-22 | `docs/` | 一次性评审复核调研（现场只读复核结论） |
 
 > 购物类文档（打印机购买指南、交换机选型调研）已按整改计划移入 Obsidian
 > vault（`~/Documents/vault/my-vault/02_Areas/House/`），不在本目录。