docs(storage-resize-images): kit README's Multiple instances section fails in an installed project #3271

storage-resize-images kit. Priority: low. Following the README's multiple-instance steps fails in an installed project, and two behaviours are undocumented.

Problems

• The "Multiple instances" firebase.json fails in a project created by firebase functions:kits:install:

  Error: Could not detect runtime for functions at <project dir>
  

  What works is the layout the install writes: source at function-kits/storage-resize-images/source with its sourcePackage and predeploy entries, and one config-<id> directory per instance, each with a full .env (including FUNCTION_DEFAULT_REGION). Running the install a second time adds an instance, but always with id storage-resize-images and an empty .env. The README mentions neither route.
• Removing one instance isn't documented. firebase functions:kits:uninstall --instance <id> removed that instance's function, Cloud Run service, Eventarc trigger, service account, config directory and firebase.json entry, and left the other instance running.
• An empty IS_ANIMATED= drops animation. It deploys without warning, and a 5-frame gif and webp both come out as one frame. The Configuration table lists the default as true. The extension can't be installed with an empty value, and by reading its parser would also treat one as false, so this is a docs gap.

Code

• Kit README: Configuration, Multiple instances.

Resolution

Rewrite "Multiple instances" around functions:kits:install and functions:kits:uninstall --instance, and note that an empty IS_ANIMATED= means false.