feat: update project version and description; add runtime state management and server routes

- Bump version to 0.6.0 and enhance project description in pyproject.toml.
- Introduce runtime state management with RuntimeCandidateState and RuntimeCandidateStateStore classes to handle candidate updates and state retrieval.
- Implement server routes for updating and reading runtime candidate states, handling various request scenarios and errors.
- Add tests for runtime layout and prompt random choice functionality, ensuring robust validation and state management.
- Enhance frontend with runtime candidate editor, including UI updates and synchronization with server state.

.github/workflows/regression-tests.yml

@@ -0,0 +1,25 @@
+name: Regression tests
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.10"
+      - uses: actions/setup-node@v4
+        with:
+          node-version: "20"
+      - name: Run Python regression tests
+        run: python -B -m unittest discover -s tests -v
+      - name: Check frontend JavaScript syntax
+        run: |
+          node --check web/prompt_random_choice.js
+          node --check web/runtime_prompt_random_choice.js
+      - name: Run frontend regression tests
+        run: node --test tests/runtime_layout.test.mjs