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/usr/local/share/terminfo-src/ghostty.terminfo

@@ -0,0 +1,14 @@
+# xterm-ghostty — alias of the maintained ncurses `ghostty` terminfo entry.
+#
+# Ghostty sets TERM=xterm-ghostty by default, but the ncurses terminfo
+# database (Debian: ncurses-term) ships the entry under the name `ghostty`
+# only — there is no `xterm-ghostty` alias, and no distro packages one. This
+# thin alias makes xterm-ghostty resolve to the same upstream-maintained
+# capability set, so SSH sessions from a Ghostty terminal work without
+# vendoring Ghostty's full (Zig-generated) terminfo here.
+#
+# `use=ghostty` is resolved by `tic` at compile time against the base
+# `ghostty` entry from ncurses-term (installed in Dockerfile.base before the
+# compile step). Compiled with `tic -x`.
+xterm-ghostty|Ghostty terminal emulator (xterm-ghostty alias),
+	use=ghostty,