Stop the Test tab claiming USB-C can measure a link

[marknolan]

Disconnected, the Test tab said this twice and disagreed with itself:

banner: Connect over BLE, Classic Bluetooth or USB-C to measure the link, run the sensor's built-in self-test, or watch its clock drift against this host.

throughput card, an inch below: Connect over BLE or Classic Bluetooth to measure the link.

The card is the one that was right. The USB-C connection speaks the dock
protocol, whose command set has no data-rate test, so it is the single link that
cannot measure anything — verify.mjs already asserts that gap directly:
WiredShimmerClient carries no runDataRateTest where Shimmer3RClient does.

What changed

The banner offers only what all three links can do, and the card keeps the
restriction — it is card-specific and was already written there. One statement
each, no contradiction, and the duplication goes with it.

The card no longer promises BLE. It now asks to connect over Bluetooth,
"BLE or Classic, whichever radio this sensor carries". The RN42 Shimmer3 fleet
has no BLE radio at all, so naming BLE is advice a classic-only sensor cannot
follow; the SDK's own platformSupport.ts is careful about exactly this, for
exactly this reason.

The hint under the button explained host-to-host variance in BLE terms only
("BLE negotiates its connection interval with the host's own Bluetooth stack").
It now gives the Classic Bluetooth half too, and states the USB-C fact in the
place a reader is already looking.

The button's tooltip repeated the hint in different words — "connection
interval and MTU on BLE, buffering on Classic Bluetooth" — so it now carries
only what the hint does not: the pipe, not the file-transfer protocol on top of
it.

README: the link table had no throughput column at all, so a reader checking
what USB-C can do would not have found the answer where the table promised it.
It has one now (yes / yes / no), with a footnote on why it is
Bluetooth-only and which Shimmer models carry which radio.

Verification

Two harness checks pinned the old strings, so they move with them — each now
asserting the substance rather than the sentence:

• the card note must name Bluetooth, say which radio, and give the dock's reason
• the banner must not say "measure" at all

Full pass green against headless Chrome: 293/293, including
disconnected it is refused with a reason, and the dock link genuinely cannot run it — Connect over Bluetooth to measure a link — BLE or Classic, whichever radio this sensor carries. The USB-C connection speaks the dock protocol, which has no data-rate test in it.

Follows #87, which renamed the test but left this copy alone.

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