Security hardening from 2026-07-01 audit

- Exclude supabase/ from Docker build context (leaked service_role key file)
- /api/files: exact per-user namespace match + reject path traversal;
  storage resolveKey rejects ".."/"." segments (fixes cross-user file read)
- Add ownsProperty/Unit/Tenant checks to tenants, maintenance (landlord path),
  and documents (JSON branch, now field-whitelisted) create handlers
- Escape user data in follow-up + payment-link emails (reuse escapeHtml)
- Neutralize CSV formula injection in toCsv + export routes
- Tighter sign-in rate limit (10/min); env-gated email verification + sender
- Per-request nonce CSP; drop script-src 'unsafe-inline' (styles unchanged)
- Add input length bounds; validate follow-ups POST body

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/api/tenants/route.ts

@@ -4,6 +4,7 @@ import { db } from "@/lib/db"
 import { tenants, units } from "@/lib/db/schema"
 import { getSessionUser } from "@/lib/session"
 import { tenantSchema } from "@/lib/validations"
+import { ownsProperty, ownsUnit } from "@/lib/db/ownership"
 import { logActivity } from "@/lib/activity"
 
 export async function GET(request: Request) {
@@ -53,6 +54,13 @@ export async function POST(request: Request) {
   const parsed = tenantSchema.safeParse(body)
   if (!parsed.success) return NextResponse.json({ error: parsed.error.flatten() }, { status: 400 })
 
+  if (
+    !(await ownsProperty(user.id, parsed.data.property_id)) ||
+    !(await ownsUnit(user.id, parsed.data.unit_id))
+  ) {
+    return NextResponse.json({ error: "Forbidden" }, { status: 403 })
+  }
+
   const [tenant] = await db
     .insert(tenants)
     .values({ ...parsed.data, user_id: user.id })