Harden session handling, add password reset/change, and firm up round polling

Session hardening: / and /admin now respond with Cache-Control: no-store, and
both pages re-derive their auth state on pageshow (event.persisted) as a
safety net against bfcache showing a stale logged-in/out view across
back/forward navigation. The user page also syncs logout across tabs via the
storage event, since localStorage is shared but in-memory JS state isn't.

Password recovery: admin gets a "Reset" button per user (POST
/admin/users/{id}/reset-password) that generates and sets a new password,
shown once — passwords are Argon2-hashed and can never be recovered, only
replaced. Users get self-service password change (POST
/users/me/change-password, requires the current password) under a new
Profilo tab, alongside read-only account info (username, address, balance,
join date).

Round display robustness: the user dashboard now refreshes immediately on
tab visibility change (background tabs get their timers throttled hard),
shows an explicit "connessione persa" state after repeated failed polls
instead of silently freezing on stale data, and polls faster both right when
the countdown hits zero and through the gap where the round is past its
deadline but still waiting for in-flight bets to confirm before the server
actually closes it.

tests/unit/test_admin.py

@@ -166,3 +166,48 @@ async def test_admin_privkey_404_for_unknown_user(client):
     headers = {"X-Admin-Token": "test-admin-token"}
     resp = await client.get("/admin/users/999/privkey", headers=headers)
     assert resp.status_code == 404
+
+
+async def test_admin_resets_user_password(client):
+    from app.auth.security import hash_password, verify_password
+    from app.db import base as db_base
+    from app.db.models import User
+    from app.wallet.hd import derive_user_address
+
+    old_hash = hash_password("original-password")
+    async with db_base.AsyncSessionLocal() as session:
+        user = User(
+            username="carol",
+            password_hash=old_hash,
+            derivation_index=2,
+            address=derive_user_address(2),
+        )
+        session.add(user)
+        await session.commit()
+        await session.refresh(user)
+        user_id = user.id
+
+    headers = {"X-Admin-Token": "test-admin-token"}
+    resp = await client.post(f"/admin/users/{user_id}/reset-password", headers=headers)
+    assert resp.status_code == 200
+    body = resp.json()
+    assert body["username"] == "carol"
+    new_password = body["new_password"]
+    assert new_password and new_password != "original-password"
+
+    async with db_base.AsyncSessionLocal() as session:
+        refreshed = await session.get(User, user_id)
+        assert refreshed.password_hash != old_hash
+        assert verify_password(new_password, refreshed.password_hash)
+        assert not verify_password("original-password", refreshed.password_hash)
+
+
+async def test_admin_reset_password_requires_token(client):
+    resp = await client.post("/admin/users/1/reset-password")
+    assert resp.status_code == 403
+
+
+async def test_admin_reset_password_404_for_unknown_user(client):
+    headers = {"X-Admin-Token": "test-admin-token"}
+    resp = await client.post("/admin/users/999/reset-password", headers=headers)
+    assert resp.status_code == 404