fix: allow profile lookup for sharing by adding RLS policy

The profiles table RLS policies only allowed users to view their own
profile, causing the share feature to fail when searching for users
by email. Added a policy allowing any authenticated user to read profiles.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

supabase/migrations/20260124100000_allow_profile_lookup_for_sharing.sql

@@ -0,0 +1,10 @@
+-- Migration: Allow authenticated users to look up profiles for sharing
+-- Problem: The profiles RLS policies only allow users to see their own profile
+-- (or admins to see all). This prevents the sharing feature from finding
+-- users by email since the query is blocked by RLS.
+-- Solution: Add a SELECT policy allowing any authenticated user to view profiles.
+
+CREATE POLICY "Authenticated users can view profiles"
+  ON profiles
+  FOR SELECT
+  USING (auth.uid() IS NOT NULL);