chore: prepare for v2.0.0 (#405)

## Summary

This PR prepares `supabase/setup-cli` for `v2.0.0`.

The main goal of this release is to simplify the action and modernize
the repo/tooling around a Bun-based implementation, while tightening
workflows, tests, and documentation.

## What Changed

### Action runtime
- switched the action from a Node/compiled `dist` runtime to a Bun-based
composite action
- removed the checked-in `dist/` output entirely
- simplified the action source down to a single runtime file in
`src/main.ts`
- kept the public action interface the same:
  - `with.version`
  - `outputs.version`

### Tooling
- switched package management and local tooling from npm to Bun
- removed Rollup and the build step
- replaced Jest with Bun’s native test runner
- replaced Prettier with `oxfmt`
- replaced ESLint with `oxlint`
- enabled type-aware/type-check linting with `oxlint-tsgolint`
- simplified TypeScript config to a single `tsconfig.json` extending
`@tsconfig/bun`

### Tests
- moved tests next to the runtime source
- rewrote tests to focus on meaningful user-facing action behavior
- added coverage for:
  - default entrypoint execution
  - latest version installs
  - legacy version installs
  - modern pinned version installs
  - failure when the installed CLI cannot report a version
- action code coverage is now `100%`

### Workflows
- renamed workflow files for clarity:
  - `test.yml` -> `ci.yml`
  - `start.yml` -> `e2e.yml`
- updated workflow/job naming so required checks are clean and stable:
  - `CI`
  - `E2E`
  - `CodeQL`
  - `Licensed`
- added aggregate PR-facing checks so branch protection does not need
matrix legs
- made CI and E2E skip heavy jobs on draft PRs
- made E2E run automatically on ready PRs and new commits
- simplified CodeQL config by removing the separate config file
- updated action pins to current releases using commit SHAs
- refined Dependabot for Bun-era updates and non-major auto-merge

### Docs
- refreshed `README.md` and `docs/index.md` for the new v2 behavior
- updated examples to use `@v2`
- added a practical example for exporting local Supabase env vars after
`supabase start`
- removed stale references to old local/dev flows

## Breaking / Notable Changes

- the action now runs as a Bun-based composite action instead of a
prebuilt JavaScript action
- no checked-in `dist/` artifacts anymore
- self-hosted runners now need the prerequisites expected by the
composite action path:
  - `bash`
- network access to install Bun/dependencies and download the Supabase
CLI

## Validation

Verified locally with:
- `bun run format:check`
- `bun run lint`
- `bun test`
- `bun run ci`

Also updated workflows and branch-protection-friendly check names so PR
validation is cleaner going forward.

## Follow-up

After merge, branch protection should require only:
- `CI`
- `E2E`
- `CodeQL`
- `Licensed`

---------

Co-authored-by: licensed-ci <licensed-ci@users.noreply.github.com>

.github/workflows/dependabot.yml

@@ -3,6 +3,10 @@ name: Dependabot auto-merge
 
 on: pull_request
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
 permissions:
   pull-requests: write
   contents: write
@@ -10,29 +14,25 @@ permissions:
 jobs:
   dependabot:
     runs-on: ubuntu-latest
-    # Checking the actor will prevent your Action run failing on non-Dependabot
-    # PRs but also ensures that it only does work for Dependabot PRs.
+    timeout-minutes: 10
+    # Only act on PRs opened by Dependabot from branches in this repository.
     if: github.actor == 'dependabot[bot]' && github.repository == github.event.pull_request.head.repo.full_name
     steps:
-      # This first step will fail if there's no metadata and so the approval
-      # will not occur.
+      # Metadata drives the non-major gating used for approval and auto-merge.
       - id: meta
         uses: dependabot/fetch-metadata@ffa630c65fa7e0ecfa0625b5ceda64399aea1b36 # v3.0.0
         with:
-          github-token: '${{ secrets.GITHUB_TOKEN }}'
+          github-token: "${{ secrets.GITHUB_TOKEN }}"
 
-      # Here the PR gets approved.
       - name: Approve a PR
-        if: ${{steps.meta.outputs.update-type != 'version-update:semver-major'}}
+        if: ${{ steps.meta.outputs.update-type != 'version-update:semver-major' }}
         run: gh pr review --approve "$PR_URL"
         env:
           PR_URL: ${{ github.event.pull_request.html_url }}
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
-      # Finally, this sets the PR to allow auto-merging for patch and minor
-      # updates if all checks pass
       - name: Enable auto-merge for Dependabot PRs
-        if: ${{steps.meta.outputs.update-type != 'version-update:semver-major'}}
+        if: ${{ steps.meta.outputs.update-type != 'version-update:semver-major' }}
         run: gh pr merge --auto --squash "$PR_URL"
         env:
           PR_URL: ${{ github.event.pull_request.html_url }}