feat(v5.2.0): finalize Infrastructure & Polish (tests isolation, xdist, lint, CI)

tests/conftest.py: mutate the settings singleton (instead of rebinding) so DB + backup dir are isolated per test -> pytest-xdist safe.
Real backup tests (snapshot/prune/admin API) and OAuth mock tests (Gitea/GitHub/link) replace the previous skips.
init_db() now also creates webhook_subscriptions (full schema without the FastAPI lifespan).
ruff check is clean; .eslintrc.json migrated to eslint.config.mjs (flat config).
CI: lint job (ruff + eslint), parallel tests (-n auto), run on every branch push.
VERSION 5.11.1.

app/services/embeds.py

@@ -147,7 +147,7 @@ def embed_src(url: str) -> str | None:
     u = urlparse(url if url.startswith("http") else "https://" + url)
     if u.scheme not in ("http", "https"):
         return None
-    host = (u.hostname or "").lower().replace("www.", "")
+    (u.hostname or "").lower().replace("www.", "")
     netloc = (u.netloc or "").lower()
     params = parse_qs(u.query)
     # Google Maps share links encode the query in the path (…&q=/maps/…)
@@ -191,4 +191,4 @@ def embed_html(src: str, *, height: int = 520) -> str:
         f'style="width:100%;height:{height}px;border:none;border-radius:8px;background:#000;" '
         f'allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; '
         f'picture-in-picture" allowfullscreen></iframe>'
-    )
+    )