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

.licenses/npm/@actions/tool-cache.dep.yml

@@ -1,20 +0,0 @@
----
-name: "@actions/tool-cache"
-version: 4.0.0
-type: npm
-summary: Actions tool-cache lib
-homepage: https://github.com/actions/toolkit/tree/main/packages/tool-cache
-license: mit
-licenses:
-  - sources: LICENSE.md
-    text: |-
-      The MIT License (MIT)
-
-      Copyright 2019 GitHub
-
-      Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
-
-      The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
-
-      THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
-notices: []

.licenses/npm/semver.dep.yml

@@ -1,26 +0,0 @@
----
-name: semver
-version: 7.7.4
-type: npm
-summary: The semantic version parser used by npm.
-homepage:
-license: isc
-licenses:
-  - sources: LICENSE
-    text: |
-      The ISC License
-
-      Copyright (c) Isaac Z. Schlueter and Contributors
-
-      Permission to use, copy, modify, and/or distribute this software for any
-      purpose with or without fee is hereby granted, provided that the above
-      copyright notice and this permission notice appear in all copies.
-
-      THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
-      WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
-      MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
-      ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
-      WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
-      ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR
-      IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
-notices: []