add doc about wisp skipping same CID during upload and note about sveltekit/vite chunking

docs: add blob reuse & framework caveats guide Documents the SvelteKit version hash issue that breaks Wisp's blob reuse by forcing re-upload of unchanged chunks on every deploy. Includes the fixed-version workaround and notes the tradeoff with SvelteKit's built-in cache busting. Refs #37