Install Supabase CLI from npm (#442)

## Summary
- install the Supabase CLI through the `supabase` npm package instead of
GitHub release archives
- support npm-backed `latest`, `beta`, and fixed published versions,
with root lockfile detection preserved
- remove the `github-token` input and use Node.js/npm without clobbering
an already configured Node.js 20+ runtime
- update CI/docs for the v3 action contract and remove stale license
cache entries for removed dependencies

Addresses CLI-1480:
https://linear.app/supabase/issue/CLI-1480/source-cli-install-from-npm-registry

No earlier pull request found to supersede.

## Validation
- `bun run ci`
- real npm install spot checks for `supabase@latest`, `supabase@beta`,
`supabase@1.178.2`, `supabase@2.33.0`, and legacy `supabase@1.15.1`
preinstall handling
- external fixture run:
https://github.com/jgoux/setup-cli-testing/actions/runs/28656824691
- hosted runners: Ubuntu, macOS, and Windows for `latest`, `beta`,
`1.178.2`, and `2.33.0`
  - package-lock detection: resolved and installed `supabase@2.108.0`
  - legacy preinstall: installed `supabase@1.15.1`
- Node preservation: kept a caller-provided Node.js 22 runtime active
after the action
- Alpine 3.20 container: `latest`, `beta`, and `2.100.0`, including
Node.js 20+ and runtime dependency checks
  - Alpine 3.18 container: rejected Node.js 18 with a clear setup error

package.json

@@ -1,6 +1,6 @@
 {
   "name": "setup-cli",
-  "version": "2.0.0",
+  "version": "3.0.0",
   "private": true,
   "description": "Supabase CLI GitHub Action",
   "keywords": [
@@ -24,8 +24,7 @@
     "typecheck": "bun x tsgo -p tsconfig.json --noEmit"
   },
   "dependencies": {
-    "@actions/core": "^3.0.1",
-    "@actions/tool-cache": "^4.0.0"
+    "@actions/core": "^3.0.1"
   },
   "devDependencies": {
     "@tsconfig/bun": "^1.0.10",