Add ACMCC app source, Supabase backend, and project config

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

supabase/migrations/20260507173902_f3bbf7cd-6cf9-4824-ae4f-ca3ceefccdf0.sql

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+ALTER TABLE public.profiles ADD COLUMN IF NOT EXISTS username text;
+
+-- Format check: 3-32 chars, alphanumeric + . _ -
+ALTER TABLE public.profiles DROP CONSTRAINT IF EXISTS profiles_username_format_chk;
+ALTER TABLE public.profiles ADD CONSTRAINT profiles_username_format_chk
+  CHECK (username IS NULL OR username ~ '^[A-Za-z0-9._-]{3,32}$');
+
+-- Case-insensitive uniqueness
+CREATE UNIQUE INDEX IF NOT EXISTS profiles_username_lower_unique_idx
+  ON public.profiles (lower(username))
+  WHERE username IS NOT NULL;
+
+-- Lookup email by username (used by the login screen)
+CREATE OR REPLACE FUNCTION public.lookup_email_by_username(_username text)
+RETURNS text
+LANGUAGE sql
+STABLE SECURITY DEFINER
+SET search_path TO 'public'
+AS $$
+  SELECT p.email
+  FROM public.profiles p
+  WHERE lower(p.username) = lower(_username)
+  LIMIT 1
+$$;
+
+GRANT EXECUTE ON FUNCTION public.lookup_email_by_username(text) TO anon, authenticated;