fix(cli): reload MCP config after project selection

[luantaraschi]

Summary

• Reload the local agent registry after the project picker changes the working directory, so the selected project's .agents/mcp.json is loaded before the client is recreated.
• Preserve the existing --agent override behavior.
• Add a regression test that verifies a project MCP server reaches the base agent definition after project selection.

Fixes #957

Testing

• Project picker and local agent registry tests: 41 passed
• CLI typecheck
• SDK build
• Freebuff Windows binary build
• Freebuff version and help E2E tests: 5 passed