feat: add database schema migrations and seed data

8 SQL migration files covering all 10 tables, RLS policies with
SECURITY DEFINER helpers, and seed data for SCW1 site + 3 zones.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AWxyMibCuGGtSQSqfajDQ7

supabase/migrations/20260709000002_users.sql

@@ -0,0 +1,40 @@
+-- supabase/migrations/20260709000002_users.sql
+CREATE TYPE user_role AS ENUM (
+  'reporter', 'supervisor', 'hse', 'capa_owner', 'management', 'admin'
+);
+
+CREATE TABLE users (
+  id         UUID PRIMARY KEY REFERENCES auth.users(id) ON DELETE CASCADE,
+  name       TEXT NOT NULL DEFAULT '',
+  email      TEXT NOT NULL DEFAULT '',
+  phone      TEXT,
+  role       user_role NOT NULL DEFAULT 'reporter',
+  department TEXT,
+  site_id    UUID REFERENCES sites(id),
+  active     BOOLEAN NOT NULL DEFAULT true,
+  created_at TIMESTAMPTZ NOT NULL DEFAULT now()
+);
+
+-- Auto-create users row when auth user signs up
+CREATE OR REPLACE FUNCTION public.handle_new_auth_user()
+RETURNS TRIGGER
+LANGUAGE plpgsql
+SECURITY DEFINER
+SET search_path = public
+AS $$
+BEGIN
+  INSERT INTO public.users (id, email, name)
+  VALUES (
+    NEW.id,
+    NEW.email,
+    COALESCE(NEW.raw_user_meta_data->>'full_name', NEW.email)
+  )
+  ON CONFLICT (id) DO NOTHING;
+  RETURN NEW;
+END;
+$$;
+
+CREATE TRIGGER on_auth_user_created
+  AFTER INSERT ON auth.users
+  FOR EACH ROW
+  EXECUTE FUNCTION public.handle_new_auth_user();