base: support modern terminals (ncurses-term + xterm-ghostty alias)

The base only shipped ncurses-base (xterm-256color, tmux), so SSHing in from
WezTerm/Alacritty/foot/Ghostty degraded to a dumb TERM fallback. Following the
maintainer's ansible common role:

- Dockerfile.base: install ncurses-term (terminfo for wezterm, alacritty,
  foot, st, base ghostty entry, and many more).
- rootfs/.../terminfo-src/ghostty.terminfo: thin xterm-ghostty alias
  (use=ghostty) — Ghostty connects as TERM=xterm-ghostty, which no distro
  packages. Compiled into the system db with 'tic -x'; build asserts it
  resolved via infocmp.
- kitty (xterm-kitty) already covered by kitty-terminfo; iTerm2 uses
  xterm-256color (ncurses-base).
- smoke-test: assert ncurses-term emulators + xterm-ghostty alias resolve.

Validated end-to-end in a throwaway container: ncurses-term brings the
entries, the alias compiles and equals the ghostty capability set. hadolint
clean, bash -n OK. Base-affecting, rebuilds base-<hash>. No tag.

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,