Agent traffic to the .md and llms.txt surfaces is measurable

## Summary

The site is agent-ready per #76, and no instrument on it can see the agent audience. Find one that works within the GitHub Pages ceiling, or record that none does.

## Motivation

The analytics added in #141 are a Cloudflare Web Analytics beacon — a script tag in the base layout. The surfaces built for agents in #264 never load that layout: a request for `/posts//index.md` or `/llms.txt` returns plain text with no HTML and no JavaScript, so it is invisible to the beacon by construction. Pages serves unproxied, so there are no server logs to fall back on and the zone HTTP analytics are empty.

The manifests shipped 2026-06-21 and the live scan passed 2026-06-22. Since then there has been no evidence that any agent has read the blog, and no way to obtain any. A publishing surface nobody can measure can't be evaluated or improved.

## Scope

- Enumerate what can observe non-HTML, non-JavaScript fetches on bare GitHub Pages. This is the investigation, not a known list.
- Evaluate whether proxying the site through Cloudflare (alunduil-infrastructure#7) makes zone HTTP analytics non-empty — per-path request counts for `/posts//index.md`, `/llms.txt`, and `/robots.txt`, ideally with a user-agent breakdown.
- Weigh the answer against the migration cost, given that the same move also unblocks `Link:` headers and `Accept: text/markdown` negotiation from #76.
- Decide: land a measurement, or record that the agent audience stays unmeasurable at the current hosting ceiling and close.

## Acceptance criteria

- [ ] Recorded, per instrument, whether it can see requests for `/posts//index.md`, `/llms.txt`, and `/robots.txt` on the current hosting.
- [ ] Either agent-surface request counts are readable somewhere, or a decision is recorded that they aren't, naming what would have to change.

## Additional context

- #76 — the agent-readiness manifests and the recorded GitHub Pages ceiling
- #264 — the `llms.txt` and per-post `index.md` endpoints this would measure
- #141 — the beacon these surfaces bypass
- #142 — read-count consumers, which today only ever see the human audience
- #289 — the post that surfaced the gap
- alunduil-infrastructure#7 — the Pages to Cloudflare move that may be the only unblock