Harbor: register browser MCP tools for the default local runtime

Problem

The default local-browser adapter emits CDP environment variables but no environment.mcp_servers. Kernel tasks already register pinned Playwright MCP. Harbor's stock Claude Code and Codex consume task MCP configuration to install browser tools; a CDP URL alone does not register those tools. This leaves the default browser mode without the same out-of-box tool configuration.

Scope / acceptance

• Emit the existing pinned Playwright MCP definition for both local and Kernel tasks, pointing at the existing recorded CDP session (http://127.0.0.1:9223).
• Preserve Kernel-only environment and lifecycle hooks.
• Load all V2 tasks in both modes with Harbor 0.22.0 and 0.23.0 and assert the MCP configuration survives Harbor parsing.
• Document that only agents consuming task MCP configuration are covered; do not claim every Harbor agent is end-to-end verified.

Child of #331; independent of #353 schema/staging hardening and #346 readiness changes. No new mandatory CI or image publication requirement.

@Perry2004 please review the default local-browser tool contract and the implementation PR linked below.

Locate the default local-browser adapter and the Kernel task MCP registration, then compare their task environment generation and Harbor parsing entry points. Load V2 tasks under Harbor 0.22.0 and 0.23.0 in both modes; done means the pinned Playwright MCP definition uses the recorded CDP session, Kernel-only hooks remain unchanged, and the supported agent scope is documented.