fix(spa): repair a bypassed page in seconds, not half a minute

The repair worked but arrived too late to help: about thirty seconds after a
hard reload, by which time four downloads had been started and hung, and the
page reloading under them read as an unexplained refresh.

Two delays, both removed.

`_claimController` waited its whole control budget before asking for the claim.
A page that is uncontrolled while an active worker exists will never be claimed
on its own -- a document fetched by a hard reload is exactly that shape -- so
the fifteen seconds were spent waiting for something that was not coming. The
claim is now asked for first; waiting is the fallback, not the opening move.
Measured in the harness: 6042ms of a 6000ms budget before, milliseconds after.

And a download that starts while the self-test is still running now waits for
it rather than racing it. Otherwise the click spends both its attempts failing
on a path that is about to be repaired, which is what put four frozen rows on
screen.

Hub suite 836 passed. Both new cases were checked against the unfixed source.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HCGdheDLxGReuKHga3BtST

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