Add comprehensive GitHub Actions CI/CD workflows

Implemented automated testing and quality assurance pipelines:

Workflows added:
- python-package.yml: Main CI pipeline
  * Multi-OS testing (Ubuntu, Windows, macOS)
  * Python 3.9-3.12 compatibility testing
  * Linting with flake8
  * Code formatting checks with black
  * Type checking with mypy
  * Import and compilation tests
  * Unit tests for core components

- codeql.yml: Security scanning
  * Weekly automated security analysis
  * CodeQL vulnerability detection
  * Extended security and quality queries

- dependency-review.yml: Dependency safety
  * Automatic dependency vulnerability checks
  * License compliance verification
  * Blocks moderate+ severity issues

- pr-labeler.yml: PR automation
  * Auto-labels based on changed files
  * PR size labeling (xs/s/m/l/xl)
  * Metadata extraction for better organization

- welcome.yml: Community engagement
  * Welcomes first-time contributors
  * Provides helpful guidelines
  * Improves contributor experience

Configuration:
- labeler.yml: Label mapping for automatic categorization

All workflows include proper permissions and error handling.

.github/workflows/welcome.yml

@@ -0,0 +1,35 @@
+name: Welcome
+
+on:
+  issues:
+    types: [opened]
+  pull_request_target:
+    types: [opened]
+
+jobs:
+  welcome:
+    runs-on: ubuntu-latest
+    permissions:
+      issues: write
+      pull-requests: write
+
+    steps:
+    - uses: actions/first-interaction@v1
+      with:
+        repo-token: ${{ secrets.GITHUB_TOKEN }}
+        issue-message: |
+          👋 Thanks for opening your first issue! We appreciate your contribution to the Eugen Twitch Bot project.
+
+          Please make sure you've provided all the necessary information and followed our issue template (if applicable).
+
+          A maintainer will review your issue soon!
+        pr-message: |
+          🎉 Thanks for opening your first pull request! We're excited to review your contribution.
+
+          Before we can merge, please make sure:
+          - [ ] Your code follows our style guidelines
+          - [ ] You've tested your changes
+          - [ ] You've updated documentation if needed
+          - [ ] All CI checks pass
+
+          A maintainer will review your PR as soon as possible. Thanks for contributing to Eugen!