[kpal81xd]

Refs #119. Needs playcanvas/editor#2340.

Changes

• New project tools: list_projects, get_project, open_project, create_project (with optional open: true) and update_project. All of them go through the connected Editor tab, and there is no delete.
• open_project and create_project with open: true wait for the Editor to reload and reconnect, then return get_project. Opening the project that's already open skips the reload.
• create_project takes owner as a username. It doesn't open a project the backend is still setting up, and returns meta.initializing instead.
• The branch tools' reload-and-reconnect helper moved to src/tools/reload.ts and takes its follow-up query as a parameter. Branch behaviour is unchanged.
• The Editor now sends project in its register frame. On the blank /editor page this is null, and calls to other tools there return "No project is open…" instead of the generic unsupported-method error.
• README and plugin README describe the project tools, connecting from the project manager, and what they do with your session. The context-cost figure is now ~43k (130 tools).

Tested end to end

I ran this branch as the agent against playcanvas.com, with the Editor PR loaded through use_local_frontend: list, get, create, update, open (including from the blank page), create with open: true, reconnecting after the reload, the no-project errors, and backend error pass-through. All of them behaved as described. Details are in playcanvas/editor#2340.

Manual smoke test

1. With the Editor PR deployed, open playcanvas.com/editor and connect from the MCP button next to NEW PROJECT. Expected: the button shows Connected.
2. Ask the agent to add a cube to the scene. Expected: it says no project is open and suggests listing or opening one.
3. Ask the agent to open one of your projects. Expected: the tab moves into the project and the agent confirms which project is now open.
4. Ask the agent to create a project named "Spinning Cube Demo", open it, and add a spinning cube. Expected: the new project opens in the tab and the cube is added there.
5. Ask the agent to switch branches. Expected: it behaves as before, reloading and reporting the new branch.