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/api/types.ts

@@ -16,6 +16,7 @@ export type Metadata = {
     }
     machineId?: string
     claudeSessionId?: string
+    codexSessionId?: string
     tools?: string[]
     slashCommands?: string[]
     homeDir: string
@@ -44,6 +45,7 @@ export const MetadataSchema = z.object({
     }).optional(),
     machineId: z.string().optional(),
     claudeSessionId: z.string().optional(),
+    codexSessionId: z.string().optional(),
     tools: z.array(z.string()).optional(),
     slashCommands: z.array(z.string()).optional(),
     homeDir: z.string(),