ci: add GitHub Actions test workflow + README badge

Runs pytest tests/ on every push and PR. Ubuntu runner with
Python 3.11, libmpv, and QT_QPA_PLATFORM=offscreen for headless
Qt. Badge in README links to the Actions tab.

117 tests, ~0.2s locally. CI time depends on PySide6 install
(~2 min) + apt deps (~30s) + tests (~1s).

.github/workflows/tests.yml

@@ -0,0 +1,18 @@
+name: tests
+on: [push, pull_request]
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: '3.11'
+      - name: Install system deps
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y libmpv-dev libegl1 libxkbcommon0
+      - name: Install Python deps
+        run: pip install -e . pytest
+      - name: Run tests
+        run: QT_QPA_PLATFORM=offscreen pytest tests/ -v

README.md

@@ -1,5 +1,7 @@
 # booru-viewer
 
+[![tests](https://github.com/pxlwh/booru-viewer/actions/workflows/tests.yml/badge.svg)](https://github.com/pxlwh/booru-viewer/actions/workflows/tests.yml)
+
 A booru client for people who keep what they save and rice what they run.
 
 Qt6 desktop app for Linux and Windows. Browse, search, and archive Danbooru, e621, Gelbooru, and Moebooru. Fully themeable.