feat: implement centralized artifact storage with session isolation

Add comprehensive artifact storage system with session-specific directories:

- Add --artifact-dir CLI option and PLAYWRIGHT_MCP_ARTIFACT_DIR env var
- Create ArtifactManager class for session-specific artifact organization
- Implement ArtifactManagerRegistry for multi-session support
- Add tool call logging with JSON persistence in tool-calls.json
- Update screenshot, video, and PDF tools to use centralized storage
- Add browser_configure_artifacts tool for per-session control
- Support dynamic enable/disable without server restart
- Maintain backward compatibility when artifact storage not configured

Directory structure: {artifactDir}/{sessionId}/[artifacts, videos/, tool-calls.json]

🤖 Generated with [Claude Code](https://claude.ai/code)

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

config.d.ts

@@ -100,6 +100,12 @@ export type Config = {
    */
   outputDir?: string;
 
+  /**
+   * The directory to save all screenshots and videos with session-specific subdirectories.
+   * When set, all artifacts will be saved to {artifactDir}/{sessionId}/ with tool call logs.
+   */
+  artifactDir?: string;
+
   network?: {
     /**
      * List of origins to allow the browser to request. Default is to allow all. Origins matching both `allowedOrigins` and `blockedOrigins` will be blocked.