chore: move the engine and views detail into nested AGENTS.md files

[lukecotter]

📝 Overview

The root AGENTS.md held one long paragraph with a sentence for each module, so each agent read all of it. This PR moves the engine and views detail into nested files, which an agent loads when it works in that folder. It also makes the wording shorter. No fact is removed.

🛠️ Changes

• Root AGENTS.md: 205 → 159 lines, 2,147 → 1,560 words. src/ is one short bullet per folder. engine/ and views/ point to their own file.
• New src/engine/AGENTS.md: one line per file, and the Rollups section, moved from the root.
• New src/views/AGENTS.md: one line per file.
• src/engine/CLAUDE.md and src/views/CLAUDE.md import their AGENTS.md, as benchmarks/CLAUDE.md does.
• These stay in the root, because they apply to more than one folder: the V8 object-layout rule, "event ids start at 1", Limits and Gotchas. The id and startTimestamp line moves from Rollups to Gotchas.

Check: all 187 code names in the old file are in the new files.

Claude Code loads a nested CLAUDE.md when it reads a file in that folder. Other tools can load only the AGENTS.md files from the root to their working directory. benchmarks/ works the same way.

🧩 Type of change

• 🐛 Bug fix — fixes an issue
• ✨ Feature — adds new functionality
• ♻️ Refactor — no behaviour change
• ⚡ Performance
• 📝 Docs
• 🔧 Chore — tooling, CI, deps
• 💥 Breaking change

🔗 Related issues

None.

✅ Checklist

• Tests added/updated
• pnpm run ci passes locally
• Changeset added (pnpm changeset) if this affects the published package
• Docs updated if behaviour or the public API changed

[codspeed]

Merging this PR will not alter performance

✅ 6 untouched benchmarks

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_{Comparing chore/nested-agents-md (1be0936) with main (df7726f)}