Docs: Set init/upgrade snippets to latest on latest

[kylegach]

What I did

Reverts changes in #29696, on main. Those changes only applied to next, which were then mistakenly carried over when next was copied to main in the release process.

Longer term, this situation will be fixed by https://linear.app/chromaui/issue/SB-1283/[docs]-issue-with-prereleases-and-snippet-package-labels

Checklist for Contributors

Testing

N/A - docs-only change

Documentation

• Add or update documentation reflecting your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Checklist for Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli-storybook/src/sandbox-templates.ts

• Make sure this PR contains one of the labels below:

  Available labels

  • bug: Internal changes that fixes incorrect behavior.
  • maintenance: User-facing maintenance tasks.
  • dependencies: Upgrading (sometimes downgrading) dependencies.
  • build: Internal-facing build tooling & test updates. Will not show up in release changelog.
  • cleanup: Minor cleanup style change. Will not show up in release changelog.
  • documentation: Documentation only changes. Will not show up in release changelog.
  • feature request: Introducing a new feature.
  • BREAKING CHANGE: Changes that break compatibility in some way with current major version.
  • other: Changes that don't fit in the above categories.

Greptile Summary

Updates initialization and upgrade command documentation to use @latest instead of @next version tags in the main branch, ensuring users get the stable release version by default.

• Modified docs/_snippets/init-command.md to use @latest for npm command: npx storybook@latest init
• Modified docs/_snippets/init-command.md to use @latest for pnpm command: pnpm dlx storybook@latest init
• Modified docs/_snippets/init-command.md to use @latest for yarn command: yarn dlx storybook@latest init
• Updated corresponding upgrade commands in docs/_snippets/storybook-upgrade.md to use @latest tag

[greptile-apps]

LGTM

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