fix(refresh): only 200 is a page, so a 202 challenge names itself

The health check earned its keep on the first run: six sources broken, four
cycles each, "last confirmed never" — and a last status of **202**. That is
game8.co's edge answering a GitHub runner with a bot-management body instead of
the wiki.

`response.ok` admitted it. A 202 therefore passed the status gate as a
document, reached the parser, yielded nothing, and was reported as "kept
previous snapshot; new body yielded 0 events" — an accurate description of the
symptom that never mentioned the status explaining it, which is why this looked
like a parser problem for days. Require 200: 202 means the request was accepted
for processing, 204 has no body, 206 is a fragment, and none of them is a page.
The rejection note already names the Server header, so the next cycle reads
`HTTP 202 (AkamaiGHost)` instead.

Recorded in CLAUDE.md § Scraping conduct, including that this must not be worked
around. The per-host spacing added alongside does not help and was never going
to — a 202 on a cycle's first request is address reputation, not rate. Browser
-shaped headers or a residential egress would be defeating an access control,
which is the ground uma.moe was declined on, and game8's robots.txt is
permissive, which makes doing it there worse rather than better.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

docs/INGESTION.md

@@ -177,6 +177,11 @@ section but must never claim the event title.
   permission we have. A 404 means no restrictions.
 - 20s timeout. **No retries**: a retry is a second request, and CLAUDE.md § Scraping conduct says
   one per source per cycle. A failed source waits for the next cycle instead.
+- **Only `200` is a page** (plus `304` for "unchanged"). Not `response.ok` — that admits the whole
+  2xx range, and `202 Accepted` is what an edge bot-manager answers with while it serves a challenge
+  instead of the wiki. Admitting it fed that challenge page to the parser, which reported "yielded 0
+  events" — the symptom, with the status that explained it unmentioned. `204` has no body and `206`
+  is a fragment; none of them is a document.
 - **Space requests to a host we have already asked this cycle** — the host's `Crawl-delay` if it
   states one, else `DEFAULT_HOST_GAP_MS` (2s). The wait is taken after the interval and robots gates,
   so a source we then skip costs nothing.