fix(spa): stop reloading a healthy page at boot

Reported from Chrome: connecting to a group triggered a page refresh within
seconds, taking the WebRTC session down with it.

The boot check added with the bypass repair asked its question by *performing a
download* -- a four-byte stream through a hidden iframe. Chrome rations the
downloads a page may start without a user gesture to about three, measured: on
a first visit three consecutive attempts went served, served, refused. So the
check competed with the person's own downloads for that budget, and its answer
depended on how much of the budget was left. On a healthy page it concluded the
worker could not serve, and reloaded.

The same mistake the repair was written to fix, from the other side: paying a
capability to obtain a diagnostic.

The replacement costs nothing and asks nothing. Measured on Chrome, at document
start, before anything registers:

    first visit       controller false, registration false
    ordinary reload   controller true,  registration true
    hard reload       controller false, registration true

Being uncontrolled while an active registration already exists names a
hard-reloaded document exactly, so that is now the whole of the evidence. A
first visit is uncontrolled too and is not a bypass -- the worker is installing
and will claim the page in a moment -- which is precisely the case that was
reloading.

Four cases, each checked against the unfixed source, including that priming
performs no download at all. Hub suite 847 passed.

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

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