docs: Fold WEB-1142 fleet-wide findings into caching/component skills

[miguelcolmenares]

Summary

A 2026-08 audit across 9 Silver Side Next.js repos (WEB-1142: error handling, plus a follow-up architecture pass) found the same handful of bugs independently, repeatedly, in codebases that never shared code. That's strong evidence these belong in the shipped guidance, not just in one repo's incident log — this PR folds them into the relevant skills, their auto-applied instruction companions, and the review checklist.

Changes Made

• nextjs-caching skill + caching.instructions.md: the notFound() → HTTP 200 gotcha (an ancestor loading.tsx locks the response status before a notFound() check resolves — reproduced live in 5+ repos), the discriminated-union data-fetching pattern (found/not_found/incomplete/api_error instead of T | null, so a transient upstream error can't get cached as a permanent 404), an explicit status-blindness warning on the CDN/edge-override caching strategy (confirmed caching a live 500 the same as a 200 in one repo), and a new preferred strategy — native ISR via generateStaticParams() { return [] }, which unlocks per-status caching on a dynamic segment with zero pages pre-built at compile time.
• component-architecture skill + react-components.instructions.md: a "one component per file" rule (found violated independently in 6+ repos — multi-export files like skeleton.tsx/menu.tsx), and the shared <JsonLD> component pattern for structured data instead of inline dangerouslySetInnerHTML script tags (found duplicated in every repo audited, plus a required-data-prop bug found in three forks of one template).
• domain-driven-design skill: a generic rule — a resolver calling a framework navigation primitive (notFound(), redirect()) belongs colocated with its route, not in lib/.
• review-code.prompt.md: new caching checklist items and a new Component Architecture checklist section covering all of the above.
• CHANGELOG.md: [Unreleased] entry summarizing the above.

Numbering in both the caching skill and instructions was preserved deliberately (0. prefix, 2c/2d suffixes) rather than renumbered, per this repo's own documented AGENTS.md warning that markdownlint's MD029 auto-fix previously broke prose in nextjs-caching/SKILL.md that cites items by number.

Type of Change

• 📝 Documentation

Testing

• npm run lint, npx tsc --noEmit, npm test (86/86) all pass
• npm run check (full pipeline: format, lint:md, validate:prompts, typecheck, build, lint, test) passes via the pre-push hook
• Cross-reference audit: no index/README describing these skills needed updates; no numbered cross-reference broken by the new content

Checklist

• Code follows project style guidelines
• Self-review completed (core-review pass, --budget medium)
• Documentation updated
• Tests pass locally

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