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>

lib/storage.ts

@@ -29,6 +29,9 @@ export function contentTypeForKey(key: string): string {
 /** Resolve a storage key to an absolute path, refusing path traversal. */
 function resolveKey(key: string): string {
   const clean = key.replace(/^\/+/, "")
+  if (clean.split(/[\\/]+/).some((seg) => seg === ".." || seg === ".")) {
+    throw new Error("Invalid storage path")
+  }
   const abs = path.resolve(STORAGE_DIR, clean)
   if (abs !== STORAGE_DIR && !abs.startsWith(STORAGE_DIR + path.sep)) {
     throw new Error("Invalid storage path")