fix(desktop): normalize loopback host for HTTP writes and stop Reminders nav flicker

[wpfleger96]

Two independent desktop fixes, surfaced together while dogfooding the reminder flow against a local relay.

Fix 1 — loopback host normalization

The desktop talks to the relay over two transports: WebSocket (subscriptions) and HTTP REST (every write). On macOS, localhost resolves to both ::1 and 127.0.0.1. A local relay binds 0.0.0.0:3000 (IPv4 only), so nothing listens on ::1:3000. The WebSocket client dials 127.0.0.1 directly and connects, but reqwest's happy-eyeballs tries ::1 first for HTTP writes — the connection is refused, is_connect() is true, and classify_request_error emits relay unreachable: could not connect to relay. The result is a desktop that connects over WS but fails every create_channel/submit_event against a local relay.

relay_http_base_url now rewrites an exact localhost host to 127.0.0.1 when deriving the HTTP base, so reqwest never attempts ::1. Scoped strictly to the loopback case:

• only the host segment is rewritten, and only when it is exactly localhost (port and path preserved);
• remote ws:///wss:// hosts and IP literals are untouched;
• both the ws:// → http:// and wss:// → https:// arms normalize identically;
• localhost.evil.com is not rewritten (exact-match, not prefix/substring).

Fix 2 — Reminders nav flicker / trap

Navigating to /reminders flickered "Setting up your workspace..." and trapped the user with no in-UI back. RemindersScreen rolled its own useQuery({ queryKey: ["identity"], queryFn: getIdentity }) with no staleTime (defaults to 0). On mount it saw the cached ["identity"] entry as stale and fired a background refetch. React Query flips fetchStatus to fetching for every observer of that key — including the onboarding gate's useIdentityQuery(). The gate reads that as identityIsFetching, resolveOnboardingGateStage returns blocking, and AppReady swaps RouterProvider for the loading screen, killing the nav chrome.

RemindersScreen now consumes the shared useIdentityQuery() (which sets staleTime: Infinity), removing the second observer entirely. Navigating to /reminders no longer triggers an identity refetch, so the gate never flips to blocking. The !identityQuery.data?.pubkey guard reads identically against the shared hook's return shape; the now-unused useQuery/getIdentity imports are dropped.