Fix casing and heading levels in guides/integrations.mdx

[ArmandPhilippot]

Description (required)

Fixes headings casing, npm casing and heading levels in guides/integrations.mdx. I also updated a link to avoid a potentially confusing redirection.

• In New Ecosystem tab #13571 we merged "Publish to npm" in the "Integration guide", but some heading levels under "Creating a package" have not been updated. You can see in the v5 snapshot that some of them should be nested.
• The page was mixing casing in headings, we usually use sentence case
• The page title is used in the sidebar, and for consistency this should be sentence case as well
• We were mixing casing for npm
• https://github.com/astro-community/component-template redirects to Princesseuh's account, it can be confusing for newcomers so we should use the current URL

Related issues & labels (optional)

• Suggested label: consistency/formatting, typo/link/grammar - quick fix!

[netlify]

✅ Deploy Preview for astro-docs-2 ready!

Name	Link
🔨 Latest commit	46575fb
🔍 Latest deploy log	https://app.netlify.com/projects/astro-docs-2/deploys/69c53aedd352bf0008a1ceb1
😎 Deploy Preview	https://deploy-preview-13596--astro-docs-2.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify project configuration.

[astrobot-houston]

Lunaria Status Overview

🌕 This pull request will trigger status changes.

Learn more

By default, every PR changing files present in the Lunaria configuration's files property will be considered and trigger status changes accordingly.

You can change this by adding one of the keywords present in the ignoreKeywords property in your Lunaria configuration file in the PR's title (ignoring all files) or by including a tracker directive in the merged commit's description.

Tracked Files

File	Note
en/guides/integrations.mdx	Localization changed, will be marked as complete.

Warnings reference

Icon	Description
🔄️	The source for this localization has been updated since the creation of this pull request, make sure all changes in the source have been applied.

[delucis]

Looks great — thank you @ArmandPhilippot!