Show the node uninstall command any time

[SaladDay]

What

• Web: Nodes gets a persistent Clean up a host button that opens the existing Clean up the host dialog with the same nodeUninstallCommand, for any time (host removed earlier, retired by a reset, or never registered). The dialog's node name is now optional.
• Installer hint (deploy/node/node_spec.py, 401 branch of fetch): now a runnable sudo python3 <installer path> --uninstall --installation-id <id>.
• Docs (EN + zh, source_hash refreshed): nodes.md drops the stale command template and points at Clean up a host; it names the real installation ID sources (unit name, /etc/oac-node/<id>.json, Settings → Service and deployment → Installation details) and the Core-gone command. operations.md fixes the installation ID paragraph (no file in the deleted volume) and Protocol changes now says to archive Sessions before upgrading, since removal is refused while a node holds sandboxes.

Why

audit-node.md finding 3 (uninstall command hard to reach, stale references) and finding 5 docs (upgrade order).

Verification

• pnpm --filter @oac/web typecheck: pass
• vitest run enrollment-command.test.ts: 15 pass
• python3 -m unittest test_node_spec (new test pins the hint): pass
• node --test website/tests/translations.test.mjs: 3 pass; check-names.py: pass
• Screenshots (1440/390, EN/zh-CN) of fixture console: ~/.oac/tests/installer-polish-20261015/h/

Skipped

• Playwright nodes.spec.ts (new case added) not run locally: no Chrome channel on this host; relies on CI web-acceptance.

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