Bump the centralized terminal-history defaults: tmux scrollback 50k->100k and
PTY buffer cap 2MB->32MB (trim 1.5MB->24MB). Both remain env/settings overridable
and bounds-clamped. Worst-case 20-session buffer budget rises 40MB->640MB.
Stacked on the terminal-history config commit.
Introduce src/config/terminal-history.ts: one place for terminal scrollback,
tmux history-limit, and PTY buffer byte caps, each overridable via env var or
the settings object and bounds-clamped via resolveTerminalHistoryConfig().
Defaults match the prior hardcoded values, so this is behavior-neutral. Wires
the resolver through buffer-limits, tmux-manager (incl. a setHistoryLimit so a
settings change applies live), session, server, system-routes, session-routes,
schemas, and the config port. Adds 4 optional settings keys (terminalScrollback
Lines, tmuxHistoryLimit, terminalBufferMaxBytes, terminalBufferTrimBytes) with
bounds + a trim<=max cross-check.
Aamer Akhter