Include full abs paths of worktrees in system prompt (#32725)

Some MCP servers expose tools that take absolute paths as arguments. To
interact with these, the agent needs to know the absolute path to the
project directories, not just their names. This PR changes the system
prompt to include the full path to each worktree, and updates some tool
descriptions to reflect this.

Todo:

* [x] Run evals, make sure assistant still understand how to specify
paths for tools, now that we include abs paths in the system prompt.

Release Notes:

- Improved the agent's ability to use MPC tools that require absolute
paths to files and directories in the project.

---------

Co-authored-by: Ben Brandt <benjamin.j.brandt@gmail.com>

assets/prompts/assistant_system_prompt.hbs

@@ -27,11 +27,11 @@ If you are unsure how to fulfill the user's request, gather more information wit
 If appropriate, use tool calls to explore the current project, which contains the following root directories:
 
 {{#each worktrees}}
-- `{{root_name}}`
+- `{{abs_path}}`
 {{/each}}
 
 - Bias towards not asking the user for help if you can find the answer yourself.
-- When providing paths to tools, the path should always begin with a path that starts with a project root directory listed above.
+- When providing paths to tools, the path should always start with the name of a project root directory listed above.
 - Before you read or edit a file, you must first find the full path. DO NOT ever guess a file path!
 {{# if (has_tool 'grep') }}
 - When looking for symbols in the project, prefer the `grep` tool.