fix(release): write the cask postflight as install steps (#53)

## Summary

The release workflow installs GoReleaser `~> v2`, which now resolves to
2.19. That version deprecates `homebrew_casks.hooks.post.install`, and
the workflow's `goreleaser check` fails on any deprecated property, so
the next release would fail before building.

- The cask postflight moves to `install_steps` with `{{ .StagedPath }}`.
GoReleaser renders it as a `postflight_steps` block with the absolute
`{{staged_path}}` token, which the shared alias job's modernizer passes
through unchanged.
- GoReleaser pins in workflows move to v2.19.0, which reads
`install_steps`.

## Verification

- `goreleaser check` with 2.19.0 passes for `.goreleaser.yml`; on `main`
it fails with the deprecation.
- `goreleaser release --snapshot --clean
--skip=publish,before,sign,validate` renders each cask's
`postflight_steps` block as `run "/usr/bin/xattr", args: ["-dr",
"com.apple.quarantine", "{{staged_path}}/<binary>"]`.

<!-- twapp-session: b7acef9e-0a9c-4af5-8ab8-775953bbc6e1 -->

Model: Claude Opus 5.5 (1M context, xhigh effort) in Claude Code.

Author: piekstra

.github/workflows/arch-package.yml

@@ -31,7 +31,7 @@ jobs:
           go-version-file: ${{ matrix.go-mod }}
       - uses: goreleaser/goreleaser-action@f06c13b6b1a9625abc9e6e439d9c05a8f2190e94 # v7.2.3
         with:
-          version: v2.18.2
+          version: v2.19.0
           args: release --snapshot --clean --skip=before --config ${{ matrix.config }}
       - name: Verify both Arch architectures were rendered
         shell: bash

.github/workflows/release-build-check.yml

@@ -33,7 +33,7 @@ jobs:
       - name: Install GoReleaser
         uses: goreleaser/goreleaser-action@v6
         with:
-          version: v2.17.0
+          version: v2.19.0
           install-only: true
       - name: GoReleaser check
         run: goreleaser check

.goreleaser.yml

@@ -102,8 +102,8 @@ homebrew_casks:
     description: Spotify from the command line
     hooks:
       post:
-        install: |
-          system_command "/usr/bin/xattr", args: ["-dr", "com.apple.quarantine", "#{staged_path}/sptfy"]
+        install_steps: |
+          run "/usr/bin/xattr", args: ["-dr", "com.apple.quarantine", "{{ .StagedPath }}/sptfy"]
     caveats: |
       Create a Spotify application, then run:
         sptfy init --client-id YOUR_CLIENT_ID