feat(deploy): support systemd --user process manager for nextjs-ssr

[keypair34]

Add an optional process_manager field to the nextjs-ssr deploy config. When set to "systemd", the deploy restarts the app via a git-owned systemctl --user restart <pm2_app>.service (no sudo, XDG_RUNTIME_DIR set, aborts if the unit is missing) instead of pm2. Default/"pm2" is unchanged.

This replaces the pm2 daemon model that could leave an orphaned next-server holding the port after a restart (the karokowe.com gateway-timeout outage); a systemd --user unit is cgroup-supervised so restart reaps the whole tree, and linger makes it boot-persistent with no pm2 save.

• model: process_manager: Option on DeployConfig and Project
• config: merge deploy_config.process_manager into project
• deploy: restart_stanza() helper branches pm2 vs systemd, injected into the deploy script; unit tests for both branches
• docs: smbcloud-deploy-nextjs skill "Process manager: systemd --user"

Related Issue

Fixes #

Description

Type of Change

• Bug fix
• New feature
• Refactor (no functional change)
• Documentation update
• CI / tooling change

How Has This Been Tested?

• cargo test --all-features
• Manual testing (smb <command>)

Checklist

• cargo check --workspace passes
• cargo clippy --workspace --tests -- -D warnings passes
• cargo fmt --all -- --check passes
• No new unwrap() or expect() calls in production code
• No new mod.rs files introduced
• New dependencies added to root Cargo.toml and inherited with { workspace = true }
• Error messages are user-friendly and surfaced to the terminal

Release Notes