fix(arcade): give ncurses games a TERM so they launch

The 80s arcade classics (Space Invaders/nInvaders, Pac-Man/pacman4console,
Tetris/tint, Moon Patrol/moon-buggy) are ncurses programs: initscr() fails
with "Error opening terminal" when TERM is unset. Game subprocesses were
built with exec.Command and no Env, so they inherited the agentbbs systemd
daemon's environment — which has no TERM — and every game exited before
drawing a frame. DOOM was unaffected because doom-ascii writes ANSI directly
and never touches terminfo.

Thread the client PTY's TERM through plugin.Context and hand each sandboxed
game a curated environment (TERM, PATH, HOME, LANG=C.UTF-8) instead of the
daemon's. Curating the env also stops leaking operator secrets (e.g.
COINPAY_API_KEY) into third-party game binaries.

Verified live on bbs.profullstack.com: Space Invaders and Pac-Man now render;
previously all four died instantly.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

cmd/agentbbs/main.go

@@ -406,6 +406,9 @@ func (a *app) teaHandler(s ssh.Session) (tea.Model, []tea.ProgramOption) {
 	go func() { <-s.Context().Done(); _ = a.st.EndSession(sessID) }()
 
 	ctx := plugin.Context{Store: a.st, Sandbox: a.sandbox, AssetsDir: a.assets, Host: a.host}
+	if pty, _, ok := s.Pty(); ok {
+		ctx.Term = pty.Term // ncurses arcade games need the client's TERM
+	}
 	if u.Kind != auth.Guest {
 		ctx.DataDir = filepath.Join(a.dataDir, "users", u.Name)
 		_ = os.MkdirAll(filepath.Join(ctx.DataDir, "wads"), 0o755)