feat(git): add git_diff tool for branch comparison

Added new git_diff tool to allow comparison between branches or commits.
This adds the ability to compare branches directly through the MCP interface.

src/git/README.md

@@ -26,34 +26,41 @@ Please note that mcp-server-git is currently in early development. The functiona
      - `repo_path` (string): Path to Git repository
    - Returns: Diff output of staged changes
 
-4. `git_commit`
+4. `git_diff`
+   - Shows differences between branches or commits
+   - Inputs:
+     - `repo_path` (string): Path to Git repository
+     - `target` (string): Target branch or commit to compare with
+   - Returns: Diff output comparing current state with target
+
+5. `git_commit`
    - Records changes to the repository
    - Inputs:
      - `repo_path` (string): Path to Git repository
      - `message` (string): Commit message
    - Returns: Confirmation with new commit hash
 
-5. `git_add`
+6. `git_add`
    - Adds file contents to the staging area
    - Inputs:
      - `repo_path` (string): Path to Git repository
      - `files` (string[]): Array of file paths to stage
    - Returns: Confirmation of staged files
 
-6. `git_reset`
+7. `git_reset`
    - Unstages all staged changes
    - Input:
      - `repo_path` (string): Path to Git repository
    - Returns: Confirmation of reset operation
 
-7. `git_log`
+8. `git_log`
    - Shows the commit logs
    - Inputs:
      - `repo_path` (string): Path to Git repository
      - `max_count` (number, optional): Maximum number of commits to show (default: 10)
    - Returns: Array of commit entries with hash, author, date, and message
 
-8. `git_create_branch`
+9. `git_create_branch`
    - Creates a new branch
    - Inputs:
      - `repo_path` (string): Path to Git repository
@@ -66,7 +73,7 @@ Please note that mcp-server-git is currently in early development. The functiona
 ### Using uv (recommended)
 
 When using [`uv`](https://docs.astral.sh/uv/) no specific installation is needed. We will
-use [`uvx`](https://docs.astral.sh/uv/guides/tools/) to directly run *mcp-server-git*.
+use [`uvx`](https://docs.astral.sh/uv/guides/tools/) to directly run _mcp-server-git_.
 
 ### Using PIP
 
@@ -99,6 +106,7 @@ Add this to your `claude_desktop_config.json`:
   }
 }
 ```
+
 </details>
 
 <details>
@@ -112,6 +120,7 @@ Add this to your `claude_desktop_config.json`:
   }
 }
 ```
+
 </details>
 
 ### Usage with [Zed](https://github.com/zed-industries/zed)
@@ -131,6 +140,7 @@ Add to your Zed settings.json:
   }
 ],
 ```
+
 </details>
 
 <details>
@@ -146,6 +156,7 @@ Add to your Zed settings.json:
   }
 },
 ```
+
 </details>
 
 ## Debugging