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/20260709000001_sites_zones.sql

@@ -0,0 +1,19 @@
+-- supabase/migrations/20260709000001_sites_zones.sql
+CREATE TABLE sites (
+  id      UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+  name    TEXT NOT NULL,
+  address TEXT,
+  region  TEXT,
+  active  BOOLEAN NOT NULL DEFAULT true,
+  created_at TIMESTAMPTZ NOT NULL DEFAULT now()
+);
+
+CREATE TABLE zones (
+  id             UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+  site_id        UUID NOT NULL REFERENCES sites(id) ON DELETE CASCADE,
+  name           TEXT NOT NULL,
+  qr_code_token  TEXT NOT NULL UNIQUE DEFAULT gen_random_uuid()::TEXT,
+  created_at     TIMESTAMPTZ NOT NULL DEFAULT now()
+);
+
+CREATE INDEX zones_site_id_idx ON zones(site_id);