feat: add threaded comments with polymorphic targets and slug-based routing

Introduce `load_comments` helper supporting polymorphic target types (post, project, bug) with nested parent-child threading. Refactor comment creation to use `target_type`/`target_uid` and `resolve_target_redirect` for correct redirects. Replace raw UID-based post/project routes with slug-aware resolution via `resolve_post`/`resolve_project` and `make_combined_slug`. Update SEO, sitemap, and FAB styling to use slugs and hardcoded red accent. Add reusable `_comment_section.html` template.

tests/conftest.py

@@ -6,6 +6,11 @@ PROJECT_ROOT = Path(__file__).resolve().parent.parent
 BASE_URL = "http://127.0.0.1:10501"
 SCREENSHOT_DIR = Path("/tmp/devplace_test_screenshots")
 
+_TEST_DB = tempfile.NamedTemporaryFile(suffix=".db", delete=False)
+_TEST_DB.close()
+os.environ["DEVPLACE_DATABASE_URL"] = f"sqlite:///{_TEST_DB.name}"
+os.environ["SECRET_KEY"] = "test-secret-key"
+
 
 def save_failure_screenshot(page, test_name):
     SCREENSHOT_DIR.mkdir(parents=True, exist_ok=True)
@@ -32,21 +37,19 @@ def pytest_runtest_makereport(item, call):
                 except Exception:
                     pass
 
+
 @pytest.fixture(scope="session")
 def test_db_path():
-    tmp = tempfile.NamedTemporaryFile(suffix=".db", delete=False)
-    tmp.close()
-    yield tmp.name
+    yield _TEST_DB.name
     try:
-        os.unlink(tmp.name)
+        os.unlink(_TEST_DB.name)
     except OSError:
         pass
 
+
 @pytest.fixture(scope="session")
 def app_server(test_db_path):
     env = os.environ.copy()
-    env["DEVPLACE_DATABASE_URL"] = f"sqlite:///{test_db_path}"
-    env["SECRET_KEY"] = "test-secret-key"
     env["PYTHONUNBUFFERED"] = "1"
     proc = subprocess.Popen(
         [sys.executable, "-m", "uvicorn", "devplacepy.main:app",