fix: use getSession() in useAuth hook (fixes 10s timeout)

PR #5 switched client components to getSession() but missed
src/hooks/use-auth.ts. The auth hook was still calling
supabase.auth.getUser() which makes a network round-trip to
Supabase, and on some deployments the request was hanging long
enough to trigger the 10-second safety timeout:

  [browser] [useAuth] getUser() timed out after 10s, clearing loading state

This caused the dashboard to sit on the loading spinner for the
full 10 seconds on every page load.

Changes:
- Replaced getUser() with getSession() in init() — reads from
  localStorage synchronously (no network).
- Reduced safety timer from 10s to 3s. getSession() shouldn't take
  more than a few hundred ms; 3s is a reasonable ceiling.

Security note (same reasoning as PR #5):
- The middleware server-side STILL uses getUser() to verify the JWT
  against Supabase on every request, so unauthenticated users can't
  reach protected routes.
- RLS on the database is the actual authorization boundary.
- getSession() on the client is only used to decide what UI to render.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/hooks/use-auth.ts

@@ -20,13 +20,14 @@ export function useAuth() {
     const supabase = createClient();
     let mounted = true;
 
-    // Safety net: if something hangs, surface it instead of an infinite spinner.
+    // Safety net: 3s is plenty for localStorage reads. If it hangs here,
+    // something else is wrong (likely storage permissions in an iframe).
     const safetyTimer = setTimeout(() => {
       if (mounted) {
-        console.warn("[useAuth] getUser() timed out after 10s, clearing loading state");
+        console.warn("[useAuth] getSession() timed out after 3s, clearing loading state");
         setLoading(false);
       }
-    }, 10000);
+    }, 3000);
 
     const fetchProfile = async (userId: string) => {
       try {
@@ -57,23 +58,25 @@ export function useAuth() {
 
     const init = async () => {
       try {
+        // getSession() reads from localStorage — instant, no network call.
+        // The middleware already validates the JWT server-side with getUser()
+        // on every request, and RLS enforces authorization at the DB level,
+        // so the client can trust the local session for UI purposes.
         const {
-          data: { user },
+          data: { session },
           error,
-        } = await supabase.auth.getUser();
+        } = await supabase.auth.getSession();
 
         if (error) {
-          // AuthSessionMissingError is expected when not logged in — don't log as error
-          if (error.name !== "AuthSessionMissingError") {
-            console.error("[useAuth] getUser error:", error.message);
-          }
+          console.error("[useAuth] getSession error:", error.message);
         }
 
         if (!mounted) return;
-        setUser(user);
+        const currentUser = session?.user ?? null;
+        setUser(currentUser);
 
-        if (user) {
-          await fetchProfile(user.id);
+        if (currentUser) {
+          await fetchProfile(currentUser.id);
         }
       } catch (err) {
         console.error("[useAuth] init threw:", err);