fix(auth): reopen a pre-dated approval instead of auto-granting it

Replaces the activation added in ea931dc, which round 2 of the review showed was
a real weakening: on a no-SMTP instance it made a standing whitelist entry a
bearer grant — the first anonymous party to register an approved-but-unclaimed
address got an immediately usable account under that identity, with no
attestation, no admin action and no signal anywhere. The verify-time activation
had the same shape one step removed, and neither site ran the SEC-10 preset-
password guard or left an audit trail.

Keep a human in the loop instead. An approval granted before any account existed
was a decision about the ADDRESS, so registration reopens the invite
(upsert_pending_invite gains revive_approved, used only by the register worker).
The request lands in the Access-requests queue, approving it runs
_activate_user_by_email — and with it revoke_preset_password_if_unverified — and
the account activates. One mechanism, already audited, no new grant path, and
the "awaiting admin approval" copy is honest again.

The explicit commit from the previous commit still matters: with an invite
already pending, upsert returns without committing and _issue_token is gated on
SMTP, so a no-SMTP registration was still being rolled back.

Also from round 2: gate the admin notice on a fresh decision (matching the two
other upsert callers) so a retry no longer re-pings every admin, and reset the
module-level rate limiters between tests — the suite pooled every login into one
300s window and was two logins short of failing an unrelated test with a 429.

backend/tests/conftest.py

@@ -189,3 +189,20 @@ def as_user(db, override_dep, _configured):
         return TestClient(app, headers={"x-test-user": str(user.id)})
 
     return _as
+
+
+@pytest.fixture(autouse=True)
+def _reset_rate_limiters():
+    """Every RateLimiter is a module-level singleton keyed by client IP, and TestClient always
+    presents the same host — so without this the whole suite's login/register attempts pool into one
+    300s window and, past the cap, some unrelated test starts failing with a 429 depending on order.
+    Cleared before each test; a test that wants to exercise throttling can still exhaust one itself."""
+    import app.routes.auth as _auth
+    import app.routes.messages as _messages
+    import app.routes.public as _public
+    from app.ratelimit import RateLimiter
+
+    for mod in (_auth, _messages, _public):
+        for obj in vars(mod).values():
+            if isinstance(obj, RateLimiter):
+                obj.reset()