fix: update OpenNext to 1.20.12 so pages render with Next 16.4

[anurag629]

v0.7.0 went down right after it deployed. Every page threw Unexpected loadManifest(/.next/server/preview-props.json) call! (Cloudflare error 1101). Next 16.4 (#169) loads a new file, server/preview-props.json, and @opennextjs/cloudflare 1.20.10 only inlines the manifests it knows about. 1.20.12 adds that file and needs next 16.4.1 or newer. Production is back on the v0.6.2 version until this ships.

• @opennextjs/cloudflare 1.20.12
• next and eslint-config-next 16.4.2. 16.4.1 also has security fixes (GHSA-673q-mjm6-r5xr, GHSA-2464-fhr4-w9xw, GHSA-p3m5-59mp-jv5r).
• package.json 0.7.1 for the fix release
• Lockfile made with npm 10 on Node 22, with the 8 libc fields that npm 10 drops put back

How I tested this

• npm ci, npm run lint (0 errors) and npm test (251 pass)
• opennextjs-cloudflare build, then ran the built Worker with wrangler dev: the home page, all five tools, the sitemap and the share image return 200, unknown paths return 404, and the Worker log has no errors
• The same check on develop gives the production error: 500 with Unexpected loadManifest(/.next/server/preview-props.json) call!