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

.github/workflows/e2e.yml

@@ -47,6 +47,8 @@ jobs:
         exclude:
           - version: 1.178.2
             pg_major: 17
+          - version: latest
+            pg_major: 14
     steps:
       - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
         with: