feat: cost confirmation flows

[gregnr]

We need to be crystal clear on which tools incur additional costs and we need users to confirm their understanding before running them. To do this we add two new tools:

• get_cost
• confirm_cost

Flow

1. The LLM calls get_cost to understand the cost of a new project or new branch (this will depend on the org plan and how many existing projects are in that org).

   The rules for new projects are:

   • Free org: cost will be $0/month (if the user reaches their 2 project limit, create_project will return an error)
   • Paid org with 0 projects: cost will be $0/month since the first project is included
   • Paid org with >0 projects: cost will be $10/month

   For new branches, cost is always $0.01344 / hour

2. The the LLM shares this information with the user, then calls confirm_cost which the user can choose to run.

3. confirm_cost returns a confirmation ID that is passed to create_project or create_branch. Both create_project or create_branch require a confirm_cost_id and will not run without them.