refactor!: remove executable packaging, distribute as source code only

BREAKING CHANGE: No longer distributing pre-built executables. Users must now run from source using Python and uv package manager.

Changes:
- Remove PyInstaller .spec files for all platforms
- Replace build-release.yml with simplified release.yml (changelog only)
- Update README.md installation instructions (source code only)
- Simplify CONTRIBUTING.md release process documentation
- Remove certifi compatibility code from image_downloader.py
- Bump version to 2.0.0 (major breaking change)

Migration guide:
Users should clone the repository and run: uv sync && uv run main.py

See README.md for detailed installation instructions.

Author: jasonma1127

.github/workflows/build-release.yml

@@ -0,0 +1,86 @@
+name: Create Release
+
+on:
+  push:
+    tags:
+      - 'v*'  # Trigger when pushing tags like v1.0.0
+  workflow_dispatch:  # Allow manual trigger
+
+permissions:
+  contents: write
+
+jobs:
+  test:
+    uses: ./.github/workflows/test.yml  # Reuse the test workflow
+
+  release:
+    name: Create Release
+    runs-on: ubuntu-latest
+    needs: test  # Only create release if tests pass
+    if: startsWith(github.ref, 'refs/tags/v')
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0  # Fetch all history for changelog generation
+
+      - name: Get version from tag
+        id: get_version
+        run: echo "VERSION=${GITHUB_REF#refs/tags/}" >> $GITHUB_OUTPUT
+
+      - name: Generate changelog with git-cliff
+        uses: orhun/git-cliff-action@v4
+        with:
+          config: cliff.toml
+          args: --current --strip all
+        env:
+          OUTPUT: CHANGELOG.md
+
+      - name: Prepare release body
+        id: release_body
+        run: |
+          cat > RELEASE_BODY.md << 'EOF'
+          ## 📦 Installation
+
+          This project is distributed as source code. To install and run:
+
+          ```bash
+          # Clone the repository
+          git clone https://github.com/${{ github.repository }}.git
+          cd ptcg-placeholder
+
+          # Install dependencies
+          uv sync
+
+          # Run the application
+          uv run main.py
+          ```
+
+          See the [README](https://github.com/${{ github.repository }}#readme) for detailed installation instructions.
+
+          ## 📝 What's Changed
+
+          EOF
+          cat CHANGELOG.md >> RELEASE_BODY.md
+          cat >> RELEASE_BODY.md << 'EOF'
+
+          ## 📖 Documentation
+
+          - **[README](https://github.com/${{ github.repository }}#readme)** - Installation and usage guide
+          - **[Contributing Guide](https://github.com/${{ github.repository }}/blob/master/CONTRIBUTING.md)** - For developers
+
+          ---
+
+          **⚠️ Legal Notice**: Fan-made tool for personal use only. Not affiliated with Nintendo/The Pokemon Company.
+          EOF
+
+      - name: Create Release
+        uses: softprops/action-gh-release@v1
+        with:
+          name: Pokemon Card Generator ${{ steps.get_version.outputs.VERSION }}
+          body_path: RELEASE_BODY.md
+          draft: false
+          prerelease: false
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}