feat(gitea-mcp): add create_pull_request tool

Add missing create_pull_request tool to Gitea MCP server. This completes
the PR lifecycle - previously only had list/get/review/comment tools.

- Add create_pull_request to GiteaClient
- Add async wrapper to PullRequestTools with branch permissions
- Register tool in server.py with proper schema
- Parameters: title, body, head, base, labels (optional)
- Branch-aware security: only allowed on development/feature branches

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -8,6 +8,12 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 ### Added
 
+#### Gitea MCP Server - create_pull_request Tool
+- **`create_pull_request`**: Create new pull requests via MCP
+  - Parameters: title, body, head (source branch), base (target branch), labels
+  - Branch-aware security: only allowed on development/feature branches
+  - Completes the PR lifecycle (was previously missing - only had list/get/review/comment)
+
 #### cmdb-assistant v1.1.0 - Data Quality Validation
 - **SessionStart Hook**: Tests NetBox API connectivity at session start
   - Warns if VMs exist without site assignment