fix: resolve vuetify & optional deps without relying on cwd

[AndreyYolkin]

Problem

Module setup resolved Vuetify via @vuetify/loader-shared's resolveVuetifyBase(), which hardcodes:

require.resolve('vuetify/package.json', { paths: [process.cwd()] })

This throws Cannot find module 'vuetify/package.json' whenever vuetify isn't reachable from the project cwd — i.e. pnpm isolated installs (where vuetify is only the module's own dependency, not a direct app dep) and Nuxt layers (especially external/remote layers with their own node_modules).

On Nuxt 3.16 this was a hard crash (#306). On current Nuxt it's worse: the module setup error is swallowed, so Vuetify silently fails to set up (no components/styles) with no error in the log.

The same process.cwd()-based detection (isPackageExists) silently disabled date adapters, icon packs and sass-embedded under the same layouts. The version probe (getPackageInfo('vuetify')) also degraded to '0.0.0'.

Fix

• Resolve vuetify/package.json via Nuxt's findPath (honours rootDir + modulesDir, incl. layers), falling back to the module's own dependency through import.meta.resolve — Vuetify lives next to the module in the (pnpm) virtual store and is reachable even from external layers. Mirrors the approach in @vuetify/unplugin-styles and nuxt/content#3791.
• Pass the project resolution paths (rootDir + modulesDir) to isPackageExists for date adapters / icon packs / sass-embedded.
• Drop the now-unused resolveVuetifyBase and isObject imports from @vuetify/loader-shared (still used for generateImports).
• A clear error is thrown if Vuetify genuinely can't be resolved.

Verification

• ✅ Existing suite: 27/27 (incl. layers, sass, unplugin-styles, vuetify-config).

• ✅ Real pnpm install matrix (module packed to a tarball, installed with different node-linker), before (main) vs after (fix):

  layout	before	after
  isolated, vuetify not a direct app dep (Can't install with nuxi on deno & NodeJS (pnpm) #306)	🔴 setup fails	🟢
  hoisted	🔴 (when vuetify not direct dep)	🟢
  local layers	🔴	🟢
  external layer with its own node_modules (vuetify only in the layer) (Nuxt Layers Cannot find module 'vuetify/package.json' #277)	🔴 nuxi prepare exit 1	🟢
  isolated + date adapter + icon pack	—	🟢 (detected)

  In every "before" case the exact buggy call require.resolve('vuetify/package.json', { paths: [process.cwd()] }) reproduces MODULE_NOT_FOUND.

Closes #277, #306