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/mux-interface.ts

@@ -72,6 +72,8 @@ export interface CreateSessionOptions {
   envOverrides?: Record<string, string>;
   /** Claude CLI effort level, injected as a `--settings` soft default (overridable via /effort in-session) */
   effort?: EffortLevel;
+  /** tmux history-limit (scrollback lines) to set for this session. */
+  historyLimit?: number;
 }
 
 /** Options for respawning a dead pane. */
@@ -92,6 +94,8 @@ export interface RespawnPaneOptions {
   envOverrides?: Record<string, string>;
   /** Claude CLI effort level (preserved across respawns, injected via `--settings`) */
   effort?: EffortLevel;
+  /** tmux history-limit (scrollback lines) to set for this session after respawn. */
+  historyLimit?: number;
 }
 
 /**
@@ -170,6 +174,9 @@ export interface TerminalMultiplexer extends EventEmitter {
   /** Update Ralph enabled state for a session */
   updateRalphEnabled(sessionId: string, enabled: boolean): void;
 
+  /** Apply a tmux history-limit to all tracked sessions. */
+  setHistoryLimit(limit: number): Promise<void>;
+
   // ========== Discovery ==========
 
   /**