COD-80 centralize terminal history/scrollback/buffer limits into config

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.

src/web/ports/config-port.ts

@@ -5,6 +5,7 @@
 
 import type { ClaudeMode, NiceConfig } from '../../types.js';
 import type { StateStore } from '../../state-store.js';
+import type { TerminalHistoryConfig } from '../../config/terminal-history.js';
 
 export interface ConfigPort {
   readonly store: StateStore;
@@ -15,6 +16,7 @@ export interface ConfigPort {
   getGlobalNiceConfig(): Promise<NiceConfig | undefined>;
   getModelConfig(): Promise<{ defaultModel?: string; agentTypeOverrides?: Record<string, string> } | null>;
   getClaudeModeConfig(): Promise<{ claudeMode?: ClaudeMode; allowedTools?: string }>;
+  getTerminalHistoryConfig(): Promise<TerminalHistoryConfig>;
   getDefaultClaudeMdPath(): Promise<string | undefined>;
   getLightState(): unknown;
   getLightSessionsState(): unknown[];