chore: add Docker image pull for MCP in start_ui function (#1521)

<!-- .github/pull_request_template.md -->

## Description
<!--
Please provide a clear, human-generated description of the changes in
this PR.
DO NOT use AI-generated descriptions. We want to understand your thought
process and reasoning.
-->

The MCP service which starts alongside the frontend and backend when
`cognee-cli -ui` is executed runs inside a Docker container. This setup
provides a clean and isolated environment - both for local development
and for runs initiated through the cognee CLI when installed via a pip
package.

Previously, Docker would reuse the local image by default, which could
become outdated over time.

This PR adds logic to check for a newer version of the MCP Docker image
before MCP service is executed

## Type of Change
<!-- Please check the relevant option -->
- [ ] Bug fix (non-breaking change that fixes an issue)
- [ ] New feature (non-breaking change that adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Documentation update
- [ ] Code refactoring
- [ ] Performance improvement
- [ ] Other (please specify):

## Screenshots/Videos (if applicable)
<!-- Add screenshots or videos to help explain your changes -->

## Pre-submission Checklist
<!-- Please check all boxes that apply before submitting your PR -->
- [ ] **I have tested my changes thoroughly before submitting this PR**
- [ ] **This PR contains minimal changes necessary to address the
issue/feature**
- [ ] My code follows the project's coding standards and style
guidelines
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] I have added necessary documentation (if applicable)
- [ ] All new and existing tests pass
- [ ] I have searched existing PRs to ensure this change hasn't been
submitted already
- [ ] I have linked any relevant issues in the description
- [ ] My commits have clear and descriptive messages

## DCO Affirmation
I affirm that all code in every commit of this pull request conforms to
the terms of the Topoteretes Developer Certificate of Origin.

cognee/api/v1/ui/ui.py

@@ -505,6 +505,8 @@ def start_ui(
         cwd = os.getcwd()
         env_file = os.path.join(cwd, ".env")
         try:
+            image = "cognee/cognee-mcp:main"
+            subprocess.run(["docker", "pull", image], check=True)
             mcp_process = subprocess.Popen(
                 [
                     "docker",