feat: pi-devbox parity — typst PDF, terminal terminfo, nvim colour, host-ssh check, hygiene

Ports the base additions from pi-devbox v1.4.0 + v1.5.0 that opencode-devbox
lacked (opencode-devbox already tracks pi-devbox for CLI-toolset parity, v2.6.0):

- typst PDF engine for pandoc (v1.4.0) + the pandoc typst-template default-font
  patch (v1.5.0) so 'pandoc --pdf-engine=typst' works without -V mainfont.
  pandoc shipped since v2.6.0 as a front-end only (no PDF back-end). +xz-utils.
  Tracks latest; --build-arg TYPST_VERSION escape hatch.
- Terminal support (v1.5.0): ncurses-term + kitty-terminfo + a compiled
  xterm-ghostty alias (tic -x, use=ghostty), so wezterm/alacritty/foot/ghostty/
  kitty resolve TERM over SSH instead of degrading to a dumb fallback.
- Readable Neovim colours (v1.5.0): system-wide /etc/xdg/nvim/sysinit.vim with
  termguicolors.
- Host SSH reachability check at shell startup (v1.4.0): one-time probe in
  .bash_aliases warning (with fix steps + inline pubkey) when the Mac host is
  unreachable. The rest of the LAN stack was already present.
- .claude/settings.local.json added to the gitignore_global seed (v1.5.0).
- Repo hygiene (v1.5.0): LICENSE (MIT), THIRD_PARTY.md, hadolint CI job (pinned
  v2.14.0) + .hadolint.yaml, IDEAS.md backlog.

Base-affecting (Dockerfile.base + rootfs) → base-<hash> advances, base rebuilds.
smoke-test gains typst/PDF, terminfo, and nvim-tgc assertions. Validated:
hadolint clean on both Dockerfiles, bash -n OK, base-hash guard OK, workflow
guard OK. CHANGELOG v2.7.0.

rootfs/home/developer/.bash_aliases

@@ -54,6 +54,38 @@ alias gs='git status'
 alias gd='git diff'
 alias gl='git log --oneline --graph --decorate -20'
 
+# ── Host SSH reachability check (once per container lifetime) ─────────────
+# Warns at first shell startup if the Mac host is not reachable via SSH.
+# Only runs inside a container, only if the jump key exists, and only once
+# per container lifetime (/tmp flag is cleared on recreate).
+_devbox_check_host_ssh() {
+  [ -f "/.dockerenv" ] || return 0
+  local ssh_cfg="$HOME/.ssh-local/config"
+  [ -f "$ssh_cfg" ] || return 0
+  local key_pub="$HOME/.ssh-local/devbox_jump_ed25519.pub"
+  [ -f "$key_pub" ] || return 0
+  local flag="/tmp/.devbox_host_ssh_ok"
+  [ -f "$flag" ] && return 0
+  if ssh -F "$ssh_cfg" \
+        -o BatchMode=yes \
+        -o ConnectTimeout=2 \
+        -o StrictHostKeyChecking=accept-new \
+        mac true 2>/dev/null; then
+    touch "$flag"
+    return 0
+  fi
+  local pub_key
+  pub_key=$(cat "$key_pub")
+  printf '\n\033[1;33m⚠  devbox: Mac host not reachable via SSH\033[0m\n'
+  printf '   Some tools use SSH to run commands on the Mac host.\n'
+  printf '   Fix (run both on the Mac):\n\n'
+  printf '   \033[1mStep 1\033[0m  System Settings → General → Sharing → Remote Login → ON\n\n'
+  printf '   \033[1mStep 2\033[0m  echo '"'"'%s'"'"' >> ~/.ssh/authorized_keys\n' "$pub_key"
+  printf '\n   Then open a new shell in the container to verify.\n\n'
+}
+_devbox_check_host_ssh
+unset -f _devbox_check_host_ssh
+
 # ── LAN access via the host (dssh) ───────────────────────────────────
 # When running on a VM-backed host (macOS OrbStack / Docker Desktop), the
 # entrypoint's setup-lan-access.sh generates ~/.ssh-local/config so the host