Add prepend_to_file Tool for Prepending Content to Files

Context

Adding a new prepend_to_file tool to complement the existing append_to_file tool. This provides a more efficient and explicit way to add content to the beginning of files, such as license headers, import statements, and configuration blocks.

Implementation

• Created a new tool modeled after the existing append_to_file tool with the key difference being content placement
• Implemented special handling for empty files to prevent unnecessary newlines
• Added comprehensive tests including various edge cases (empty files, different line endings, license headers)
• Integrated with existing components:
  • Updated tool registry in src/shared/tools.ts
  • Updated documentation in src/core/prompts/tools/prepend-to-file.ts
  • Updated Cline handler cases in src/core/Cline.ts
  • Updated schema definitions in src/schemas/index.ts
• Improved overall system documentation to include clear guidance on when to use prepend vs. append tools

Screenshots

No UI changes - this PR adds a new tool accessible through the AI interface.

How to Test

1. Use the AI to add a license header to a file:

   Add a license header to src/example.js
   

2. The AI should recommend using the prepend_to_file tool:

   <prepend_to_file>
   <path>src/example.js</path>
   <content>
   /**
    * Copyright (c) 2025 Roo Veterinary Inc.
    * 
    * This source code is licensed under the MIT license found in the
    * LICENSE file in the root directory of this source tree.
    */
   
   </content>
   </prepend_to_file>
   

3. Verify the content is added to the beginning of the file

4. Also test with an empty file to verify only the content is added without extra newlines