Remove only from usage instructions

[tangrufus]

Composer v2 reads available-package-patterns from repo's /packages.json.

[Copilot]

Pull request overview

Updates repository configuration examples to reflect Composer v2 behavior (reading available-package-patterns from /packages.json), removing the now-unnecessary only filter from usage instructions and related helper scripts.

Changes:

• Remove only from composer.json usage examples in README and HTML templates.
• Update the WPackagist migration script to generate a wp-packages repository entry without only.
• Adjust benchmark and canary workflow generated composer.json to omit only.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
scripts/migrate-from-wpackagist.sh	Stops injecting only into the wp-packages repository entry during migration.
internal/http/templates/roots_wordpress.html	Removes only from the displayed composer.json example.
internal/http/templates/index.html	Removes only from the displayed composer.json usage snippet.
benchmarks/resolve.sh	Removes only from generated benchmark composer.json and drops the unused pattern variable.
README.md	Updates documented composer.json examples to omit only.
.github/workflows/canary.yml	Updates the smoke-test composer.json stub to omit only.

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