feat(data): add content query helpers and LLMS builder

src/data/AGENTS.md

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+<!-- Parent: ../AGENTS.md -->
+<!-- Generated: 2026-06-30 | Updated: 2026-06-30 -->
+
+# data
+
+## Purpose
+Thin query helpers over Content Collections — draft filtering, sorting, and the experience-taxonomy aggregation.
+
+## Key Files
+| File | Description |
+|------|-------------|
+| `post.ts` | `getAllPosts()` (returns `CollectionEntry<"writing">`, drafts filtered in prod) and `groupPostsByYear()`. **Naming quirk:** file/functions say "post" but operate on the `writing` collection. |
+| `experience.ts` | `getAllExperience()` (sorted by `startDate` desc) and `getContentForExperience(id)` which gathers all `projects`/`writing`/`speaking` entries whose `experiences` include `id`. |
+| `speaking.ts` | `getAllSpeaking()` (drafts filtered in prod). |
+
+## For AI Agents
+
+### Working In This Directory
+- Draft filtering uses `import.meta.env.PROD ? !data.draft : true` — drafts are visible in dev, hidden in production.
+- `getContentForExperience` matches refs via `entry.data.experiences.some((ref) => ref.id === id)`.
+
+## Dependencies
+
+### Internal
+- `astro:content` (`getCollection`). Consumed by pages in `src/pages/` and the homepage.
+
+<!-- MANUAL: -->