refactor(codex): extract session management and launcher logic into separate modules

Reorganized runCodex.ts to improve maintainability by extracting:
- CodexSession class for session lifecycle management
- CodexLocalLauncher and CodexRemoteLauncher for mode-specific initialization
- CodexEventConverter for MCP message handling and UI buffer updates
- CodexSessionScanner for resume file discovery
- emitReadyIfIdle utility for ready event emission

Added codexSessionId field to metadata schema for session tracking.
Updated UI components to work with refactored architecture.

cli/src/codex/utils/codexEventConverter.test.ts

@@ -0,0 +1,85 @@
+import { describe, expect, it } from 'vitest';
+import { convertCodexEvent } from './codexEventConverter';
+
+describe('convertCodexEvent', () => {
+    it('extracts session_meta id', () => {
+        const result = convertCodexEvent({
+            type: 'session_meta',
+            payload: { id: 'session-123' }
+        });
+
+        expect(result).toEqual({ sessionId: 'session-123' });
+    });
+
+    it('converts agent_message events', () => {
+        const result = convertCodexEvent({
+            type: 'event_msg',
+            payload: { type: 'agent_message', message: 'hello' }
+        });
+
+        expect(result?.message).toMatchObject({
+            type: 'message',
+            message: 'hello'
+        });
+    });
+
+    it('converts reasoning events', () => {
+        const result = convertCodexEvent({
+            type: 'event_msg',
+            payload: { type: 'agent_reasoning', text: 'thinking' }
+        });
+
+        expect(result?.message).toMatchObject({
+            type: 'reasoning',
+            message: 'thinking'
+        });
+    });
+
+    it('converts reasoning delta events', () => {
+        const result = convertCodexEvent({
+            type: 'event_msg',
+            payload: { type: 'agent_reasoning_delta', delta: 'step' }
+        });
+
+        expect(result?.message).toEqual({
+            type: 'reasoning-delta',
+            delta: 'step'
+        });
+    });
+
+    it('converts function_call items', () => {
+        const result = convertCodexEvent({
+            type: 'response_item',
+            payload: {
+                type: 'function_call',
+                name: 'ToolName',
+                call_id: 'call-1',
+                arguments: '{"foo":"bar"}'
+            }
+        });
+
+        expect(result?.message).toMatchObject({
+            type: 'tool-call',
+            name: 'ToolName',
+            callId: 'call-1',
+            input: { foo: 'bar' }
+        });
+    });
+
+    it('converts function_call_output items', () => {
+        const result = convertCodexEvent({
+            type: 'response_item',
+            payload: {
+                type: 'function_call_output',
+                call_id: 'call-2',
+                output: { ok: true }
+            }
+        });
+
+        expect(result?.message).toMatchObject({
+            type: 'tool-call-result',
+            callId: 'call-2',
+            output: { ok: true }
+        });
+    });
+});