chore: remove dead code and unused exports (-159 lines)

Remove confirmed-unused code found via team-based codebase analysis:
- Dead interfaces: SessionResponse (types.ts), PlannerResult (plan-orchestrator.ts)
- Dead functions: withTimeout (session.ts), getOpenCodeAugmentedPath, resetOpenCodeCache (opencode-cli-resolver.ts)
- Dead config constants: MAX_RUN_SUMMARY_EVENTS, TRIM_RUN_SUMMARY_TO, MAX_MESSAGES_PER_CHANNEL (buffer-limits.ts), MAX_TRACKED_AGENTS, MAX_SUBAGENT_ACTIVITY_PER_AGENT, MAX_TOOL_RESULTS_PER_AGENT, COMPLETED_TODO_TTL_MS (map-limits.ts)
- Dead legacy code: idleTimer property + clearIdleTimer() no-op method + 6 call sites (respawn-controller.ts)
- Stale barrel re-exports: createAnsiPatternFull/Simple, validateTokenCounts/Cost, stripAnsi, normalizePhrase, getOpenCodeAugmentedPath (utils/index.ts)
- Un-exported internal-only symbols: ErrorMessages (types.ts), destroyRalphLoop (ralph-loop.ts)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/ralph-loop.ts

@@ -509,7 +509,7 @@ export function getRalphLoop(options?: RalphLoopOptions): RalphLoop {
 }
 
 /** Destroys the singleton instance. Use in tests or for cleanup. */
-export function destroyRalphLoop(): void {
+function destroyRalphLoop(): void {
   if (loopInstance) {
     loopInstance.destroy();
     loopInstance = null;