feat: Enhance Python environment setup with system Python option and improve dependency installation

refactor: Clean up imports in currencies and users routes
fix: Update theme settings saving logic and clean up test imports

.gitea/actions/setup-python-env/action.yml

@@ -5,30 +5,48 @@ inputs:
   python-version:
     description: Python version to install.
     required: false
-    default: "3.10"
+    default: '3.10'
+  use-system-python:
+    description: Skip setup-python and rely on the system Python already available in the environment.
+    required: false
+    default: 'false'
   install-playwright:
     description: Install Playwright browsers when true.
     required: false
-    default: "false"
+    default: 'false'
   install-requirements:
     description: Space-delimited list of requirement files to install.
     required: false
-    default: "requirements.txt requirements-test.txt"
+    default: 'requirements.txt requirements-test.txt'
   run-db-setup:
     description: Run database wait and setup scripts when true.
     required: false
-    default: "true"
+    default: 'true'
   db-dry-run:
     description: Execute setup script dry run before live run when true.
     required: false
-    default: "true"
+    default: 'true'
 runs:
   using: composite
   steps:
     - name: Set up Python
+      if: ${{ inputs.use-system-python != 'true' }}
       uses: actions/setup-python@v5
       with:
         python-version: ${{ inputs.python-version }}
+
+    - name: Verify system Python
+      if: ${{ inputs.use-system-python == 'true' }}
+      shell: bash
+      run: |
+        set -euo pipefail
+        if ! command -v python >/dev/null 2>&1; then
+          echo "Python executable not found on PATH" >&2
+          exit 1
+        fi
+        python --version
+        python -m pip --version >/dev/null 2>&1 || python -m ensurepip --upgrade
+        python -m pip --version
     - name: Configure apt proxy
       shell: bash
       run: |
@@ -59,7 +77,7 @@ runs:
         if [ -n "${requirements}" ]; then
           for requirement in ${requirements}; do
             if [ -f "${requirement}" ]; then
-              pip install -r "${requirement}"
+              python -m pip install -r "${requirement}"
             else
               echo "Requirement file ${requirement} not found" >&2
               exit 1