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>

crates/assistant_tools/src/read_file_tool.rs

@@ -31,8 +31,8 @@ pub struct ReadFileToolInput {
     /// <example>
     /// If the project has the following root directories:
     ///
-    /// - directory1
-    /// - directory2
+    /// - /a/b/directory1
+    /// - /c/d/directory2
     ///
     /// If you want to access `file.txt` in `directory1`, you should use the path `directory1/file.txt`.
     /// If you want to access `file.txt` in `directory2`, you should use the path `directory2/file.txt`.