fix(deploy): resolve host bun binary

[shuv1337]

Summary

• resolve Bun from PATH when available
• fall back to ~/.bun/bin/bun for non-interactive SSH sessions
• use the resolved executable for version validation and host builds

Root cause

The guarded host preflight assumed interactive-shell PATH initialization. Non-interactive SSH on shuvdev does not include ~/.bun/bin, so the check stopped before evaluating repository and configuration invariants.

Validation

• bash -n deploy/install-host.sh
• shellcheck deploy/install-host.sh, when available
• fallback resolution under a restricted PATH
• git diff --check
• pre-push monorepo typecheck: 32/32