fix(ssh): resolve complete remote Node/npm toolchains

[Jinwoo-H]

Summary

• require Node and npm to be runnable from the same remote toolchain directory
• skip incomplete system installations and continue to guarded NVM candidates
• preserve login-shell, version-manager, cancellation, and session-limit behavior
• add a live Ubuntu SSH/PTY regression harness for issue [Bug]: SSH relay selects system Node without npm instead of complete NVM toolchain #8450
• add the reviewed relay runtime distribution plan and living implementation checklist as a separate documentation commit

Fixes #8450

Verification

• pnpm exec vitest run --config config/vitest.config.ts src/main/ssh/ssh-remote-node-resolution.test.ts (32/32)
• pnpm exec vitest run --config config/vitest.config.ts src/main/ssh/ssh-remote-node-toolchain-resolution.test.ts (8/8)
• native-deps, versioned-install, deploy, cross-version isolation, and platform-detection focused suites (70/70)
• pnpm run typecheck
• pnpm run lint
• pnpm run check:max-lines-ratchet
• touched-file oxfmt --check
• pnpm run test:e2e:ssh-node-toolchain-resolution (Ubuntu 24.04 arm64 Docker SSH, guarded NVM selection, relay launch, PTY round-trip)

Scope

This draft contains Milestone 0 only. It does not enable or implement bundled relay runtime distribution. Existing SSH relay behavior remains the production path.

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