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_app.py

@@ -19,10 +19,25 @@ def client():
     os.environ["APP_SECRET_KEY"] = "test-secret-for-tests"
     os.environ["RATE_LIMIT_ENABLED"] = "false"
 
+    # Point the process-wide settings singleton at OUR temp DB (xdist-safe).
+    from app.config import settings
+    settings.database_url = f"sqlite:///{db_path}"
+    settings.rate_limit_enabled = False
+
     from app.db import init_db
     from app.main import app
     init_db()
 
+    # A default user id=1 so tests that reference the implicit user (favorites,
+    # workspace ownership) satisfy foreign keys without relying on leaked state.
+    from app.db import get_conn
+    with get_conn() as conn:
+        conn.execute(
+            "INSERT OR IGNORE INTO users (id, login, full_name, email, is_admin) "
+            "VALUES (1, 'tester', 'Tester', '[email protected]', 1)"
+        )
+        conn.commit()
+
     yield TestClient(app)
 
     os.unlink(db_path)
@@ -1915,7 +1930,7 @@ def test_nav_menu_workspace_pages(client):
     """/api/nav/menu returns root pages and nested children for a workspace."""
     from app.db import get_conn
     with get_conn() as conn:
-        u = conn.execute("INSERT OR IGNORE INTO users (login) VALUES ('navuser')")
+        conn.execute("INSERT OR IGNORE INTO users (login) VALUES ('navuser')")
         uid = conn.execute("SELECT id FROM users WHERE login='navuser'").fetchone()["id"]
         cur = conn.execute("INSERT INTO workspaces (name, owner_id) VALUES ('NavWS', ?)", (uid,))
         ws_id = cur.lastrowid
@@ -3294,7 +3309,7 @@ def test_v490_create_comment_with_mentions(client):
                     json={"body": "regarde ca @v4901", "anchor_block_id": "b1", "anchor_start": 0, "anchor_end": 5},
                     cookies=cookies)
     assert r.status_code == 200
-    cid = r.json()["id"]
+    r.json()["id"]
 
     r = client.get(f"/api/pages/{pid}/comments", cookies=cookies)
     assert r.status_code == 200