Phase 1 — Merge certified nodes into /integrations/

[n-lark]

Phase 1 — Make /integrations/ carry the certified story

Goal: Before we kill /certified-nodes/, make sure /integrations/ is a clearly better destination for the same audience.

New UI:

Success Criteria

• Make the "FlowFuse Certified" filter visually prominent. Today it's a single checkbox above the categories list (index.njk:347-354). Promote it to a primary toggle / pill at the top of the catalog — visible without scrolling, and obvious to a non-technical visitor.
• Add a "Certified" hero/intro module at the top of /integrations/ (or as a deep link target like /integrations/#certified) that repurposes the messaging currently on /certified-nodes/: the three pillars (Quality, Security, Support) and a link to the certified-nodes-v2 blog post.
• Verify the certified count. Toggle the filter on; expect 17 (matches both catalog.flowfuse.com and the ff-integrations API). Sort already puts certified first.
• Add a "Certified" pill/badge to tile cards when integration.ffCertified is true (cleaner than the current icon-only ff-certified-tag), so the certified story reads at a glance on the grid view.

Acceptance: A non-technical visitor landing on /integrations/ understands within ~5 seconds that FlowFuse certifies a curated set of nodes, can filter to only those, and can click into a full detail page for any of them.

Test plan:

• Toggle "Show only Certified" — count drops to 17, button shows pressed state, URL gains ?certified=1. Click again to clear.
• Sidebar checkbox and hero toggle stay in sync in either direction.
• /integrations/?certified=1 loaded directly boots with the filter applied.
• Certified filter stacks correctly with category filters and search.
• Certified tiles render the "Certified" pill; non-certified tiles don't.
• Tiles with a generated detail page (certified + top-50 by downloads) link to /integrations/{id}/ in the same tab. Tiles without (shown with the external-link icon) link to flows.nodered.org in a new tab.
• Card renders cleanly at 1280px, 768px, and 375px (stacks at 375px).
• Keyboard tab to the toggle button — focus outline is visible. Screen reader announces the integrations count when filters change (aria-live).
• No regressions: categories, search, pagination still work. Blueprints page (/blueprints/) renders correctly (shares catalog.njk).