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.

tests/test_v54.py

@@ -3,19 +3,18 @@ and v5.5.0 (embed, bookmark, video, audio, cover, icon)."""
 from __future__ import annotations
 
 import json
-import tempfile
 import os
-
-import pytest
+import tempfile
 
 # ── Helpers ──────────────────────────────────────────────────────────────
 
 
 def _login(client):
     """Create admin user and return session cookie + csrf token (like test_app.py)."""
+    import secrets
+
     from app.auth.session import SessionManager
     from app.db import get_conn
-    import secrets
 
     with get_conn() as conn:
         login = f"testadmin_{secrets.token_hex(4)}"
@@ -167,7 +166,7 @@ class TestV54VersionHistory:
         )
         data2 = r2.json()
         assert len(data2["versions"]) >= 2
-        v2_id = data2["versions"][0]["id"]
+        data2["versions"][0]["id"]
 
         # restore v1
         r3 = client.post(
@@ -191,10 +190,11 @@ class TestV54TrashPurge:
     """v5.4.0: global trash 30-day purge."""
 
     def test_trash_purge_removes_old_deleted_pages(self, client):
-        from app.services.trash import purge_expired
-        from app.db import init_db, get_conn
         import datetime
 
+        from app.db import get_conn, init_db
+        from app.services.trash import purge_expired
+
         # create temp DB
         tmp = tempfile.NamedTemporaryFile(suffix=".db", delete=False)
         tmp.close()
@@ -565,4 +565,4 @@ class TestDashboardPublicNewBlocks:
         assert "<video" in html
         assert "<audio" in html
         assert "bookmark" in html or "Ex" in html
-        assert "iframe" in html
+        assert "iframe" in html