docs: update @harperfast/nextjs plugin documentation

[Ethan-Arrowood]

Overview

Updates the reference documentation to accurately reflect the @harperfast/nextjs plugin (previously @harperdb/nextjs) and its capabilities.

Changes

New: reference/components/nextjs.md

Dedicated reference page for the @harperfast/nextjs plugin covering:

• Step-by-step setup (install, withHarper(), config.yaml, harper run)
• Using Harper Globals in server-side Next.js code
• All plugin options: bundler, dev, prebuilt, buildOnly, port, securePort, runFirst
• Harper-backed caching for ISR, Data Cache, and unstable_cache, including cacheHandlerPath(), tag invalidation, soft-invalidation model, and cache table schema

reference/components/overview.md

• Fixed all stale @harperdb/nextjs → @harperfast/nextjs references (architecture diagram, config example, Known Custom Components)
• Updated architecture diagram: nextjs shown as a plugin, not an extension
• Split Known Custom Components into Plugins and Extensions subsections
• Updated GitHub URL to HarperFast/nextjs
• Added link to new nextjs.md page

reference/components/extension-api.md

Replaced the stale @harperdb/nextjs Protocol Extension example with a generic one — @harperfast/nextjs has migrated to the Plugin API and is no longer a valid Extension API example.

reference/static-files/overview.md

Added a Dynamic Applications section at the bottom directing users who need SSR, API routes, or other dynamic behavior to consider @harperfast/nextjs.

sidebarsReference.ts

Added Next.js Plugin entry under the Components sidebar category.

Reviewer Notes

• All internal links verified via npm run build (no broken links)
• Formatting applied via npm run format:write

🤖 Generated with Claude Code

[github-actions]

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[Ethan-Arrowood]

I think having a dedicated page for Next.js in our reference docs is important for discoverability. But. I also recognize how this could sprawl quickly if we had pages for every framework we support. Maybe this belongs in a new section? Maybe the links to the readme (which this page was generated from) is sufficient? Let me know what you think. But if we don't have a docs page for it, then we can't get automatic skill generation for it (unless we go manual route or somehow start supporting multi-repo syncing lol)

[cb1kenobi]

Do we need the --save flag?

Suggested change

	npm install @harperfast/nextjs
	npm install --save @harperfast/nextjs

[kriszyp]

I think it is important enough to have a page. Are you concerned at all about drift, with this being documented both in the plugin itself and in these docs? (what is the source of truth?)