refactor: split types.ts into domain modules (phase 4, step 1)

Split 1,443-line types.ts into 14 focused domain files under src/types/:
common.ts, session.ts, task.ts, app-state.ts, respawn.ts, ralph.ts,
api.ts, lifecycle.ts, run-summary.ts, tools.ts, teams.ts, push.ts,
plan.ts, and index.ts barrel.

Moved PlanItem interface from plan-orchestrator.ts into types/plan.ts
to break circular dependency. Original types.ts replaced with barrel
re-export — zero changes to 36 import sites.

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

src/types/common.ts

@@ -0,0 +1,49 @@
+/**
+ * @fileoverview Common/shared type definitions
+ */
+
+/**
+ * Interface for objects that hold resources requiring explicit cleanup.
+ * Implementing classes should release timers, watchers, and other resources in dispose().
+ */
+export interface Disposable {
+  /** Release all held resources. Safe to call multiple times. */
+  dispose(): void;
+  /** Whether this object has been disposed */
+  readonly isDisposed: boolean;
+}
+
+/**
+ * Configuration for buffer accumulator instances.
+ * Used for terminal buffers, text output, and other size-limited string storage.
+ */
+export interface BufferConfig {
+  /** Maximum buffer size in bytes before trimming */
+  maxSize: number;
+  /** Size to trim to when maxSize is exceeded */
+  trimSize: number;
+  /** Optional callback invoked when buffer is trimmed */
+  onTrim?: (trimmedBytes: number) => void;
+}
+
+/**
+ * Resource types that can be registered for cleanup.
+ */
+export type CleanupResourceType = 'timer' | 'interval' | 'watcher' | 'listener' | 'stream';
+
+/**
+ * Registration entry for a cleanup resource.
+ * Used by CleanupManager to track and dispose resources.
+ */
+export interface CleanupRegistration {
+  /** Unique identifier for this registration */
+  id: string;
+  /** Type of resource */
+  type: CleanupResourceType;
+  /** Human-readable description for debugging */
+  description: string;
+  /** Cleanup function to call on dispose */
+  cleanup: () => void;
+  /** Timestamp when registered */
+  registeredAt: number;
+}