fix(auth): stop the address-bar mirror eating emailed auth tokens, and unlock revoked accounts

Two independent bugs made an email+password registration unrecoverable in prod.

The verification link did nothing. urlWithParams/clearParams rebuilt the URL as
pathname+query and dropped the fragment — but the one-time auth tokens ride the
fragment (#verify=/#reset=, SB3), and the providers that mirror nav params
(useUrlMirror in FeedFilters/Playlists/Plex/Channels) sit ABOVE the lazily-loaded
<App> in main.tsx. Their mount effect replaceState'd the token away before the auth
card's chunk had loaded, so the card read an empty hash: the link opened a bare
sign-in page, no request, no banner. Both helpers now carry the fragment over.

The account was then locked out for good. SEC-10 nulls password_hash when an
unverified account is attested (here: admin approval landing before the user could
verify — which the bug above made impossible). That is indistinguishable from a
Google-only account, and reset eligibility keyed off password_hash alone, so no
reset link was ever issued: no password to sign in with, and no way to get one.
users.password_revoked_at records the revocation, reset eligibility honours it, and
setting a password again (reset-confirm or set-password) clears it. An account that
never had a password stays ineligible on purpose — its owner adds one from Settings.

/auth/verify now also answers password_reset_required so the card can say why the
registered password stopped working, instead of leaving the user at the uniform
"Invalid email or password". Telling the holder of a valid verify token leaks
nothing: they have already proved they own the mailbox.

The 0078 migration backfills the stamp for rows carrying the exact lockout signature
(local, non-demo, no password, unverified), so existing victims recover unaided.

backend/app/models.py

@@ -47,6 +47,12 @@ class User(Base, TimestampMixin):
     email: Mapped[str] = mapped_column(String(320), unique=True, index=True)
     # argon2id hash for email+password login; NULL for Google-only / demo accounts.
     password_hash: Mapped[str | None] = mapped_column(String(255))
+    # When SEC-10 dropped a preset password (see auth.revoke_preset_password_if_unverified). Without
+    # this trace a revoked account was indistinguishable from a Google-only one, so it failed the
+    # password-reset eligibility check and could never be recovered — it could neither sign in nor
+    # reset. Set = "had a password, lost it to the guard" -> reset-eligible. Cleared whenever a
+    # password is set again (reset-confirm / set-password).
+    password_revoked_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True))
     # Email ownership proven (Google sign-in is implicitly verified; password registration
     # verifies via a link). Login requires this AND is_active.
     email_verified: Mapped[bool] = mapped_column(Boolean, default=False, server_default="false")