chore(apps): remove duplicate /apps landing page

[crazywriter1]

What changed? Why?

docs/apps/index.mdx is a byte-for-byte duplicate of docs/apps/quickstart/build-app.mdx, which is the page wired into the Apps nav. Two identical 548-line files served at /apps and /apps/quickstart/build-app create duplicate content (SEO) and a maintenance hazard, since edits to one silently drift from the other.

History suggests this is unintentional: build-app.mdx landed via #1363 ("updated docs"), and one day later apps/index.mdx was added in #1387 (a notifications-focused PR) with identical content, and has never been edited since.

Changes

• Delete docs/apps/index.mdx.
• Add redirects in docs.json: /apps and /apps/index → /apps/quickstart/build-app (so the /apps URL keeps working).
• Remove the now-dead /apps/index bullet from llms.txt and llms-full.txt.

Test plan

• python3 -m json.tool docs/docs.json — docs.json is valid JSON after adding the redirects.
• node scripts/lint-mdx.js all — passes; no content errors. (The default changed-files mode reports a benign File not found for the deleted page, since it diffs deleted paths; not run in CI.)
• node scripts/llms.js — confirms the only Apps-section change for this branch is dropping the /apps/index entry; build-app remains indexed.
• Reviewed history: index.mdx (Docs/notif endpoint update #1387) duplicates build-app.mdx (updated docs #1363); nav already points to build-app, so /apps is only reachable by direct URL and is now redirected — no content lost.

Notes for reviewers

• If a real landing page at /apps (rather than a redirect) is intentional, let me know and I'll instead make index.mdx a thin pointer to build-app.

[cb-heimdall]

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