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/types.ts

@@ -667,7 +667,7 @@ export enum ApiErrorCode {
 /**
  * User-friendly error messages for each error code
  */
-export const ErrorMessages: Record<ApiErrorCode, string> = {
+const ErrorMessages: Record<ApiErrorCode, string> = {
   [ApiErrorCode.NOT_FOUND]: 'The requested resource was not found',
   [ApiErrorCode.INVALID_INPUT]: 'Invalid input provided',
   [ApiErrorCode.SESSION_BUSY]: 'Session is currently busy',
@@ -711,29 +711,6 @@ export function createErrorResponse(code: ApiErrorCode, details?: string): ApiRe
   };
 }
 
-/**
- * Response for session operations
- */
-export interface SessionResponse {
-  /** Whether the request succeeded */
-  success: boolean;
-  /** Session details if successful (light state — no full buffers) */
-  session?: SessionState & {
-    /** Claude session ID from CLI */
-    claudeSessionId: string | null;
-    /** Total API cost */
-    totalCost: number;
-    /** Number of messages */
-    messageCount: number;
-    /** Whether Claude is working */
-    isWorking: boolean;
-    /** Timestamp of last prompt */
-    lastPromptTime: number;
-  };
-  /** Error message if failed */
-  error?: string;
-}
-
 /**
  * Response for quick start operation
  */