Replaces the unused, never-wired-up single contractPdfUrl field with
contractDocumentUrls (String[]) so landlords can attach several files
per contract (signed lease, addenda, ...) instead of just one. New
endpoints: GET /contracts/documents (tenant sees own contract only,
landlord sees all — same visibility rule as the rest of the app),
POST/DELETE /contracts/:id/documents (landlord/admin only). Frontend
reuses the existing FileReader-to-data-URL upload pattern already used
for inventory photos, so files are stored inline like everywhere else
in this app rather than introducing a new storage mechanism.
bernd
a8dc999180