Rebuild the Coach thinking row as one calm line

While a turn runs the Coach now shows a single row: a brain icon, the
current step in the answer's text size with a shimmer passing through it
and fading dots, and a chevron once there are steps to open. There is no
running clock any more, and the interim table preview with its sparkline
no longer renders under the row; interim tables stay in state until the
answer's own results show them.

When the answer is done the row reads "Thought process · N steps" with
proper plurals, and "Answer needed" while a clarifying question waits.
It never opens by itself, and a row opened during the run closes when
the turn ends. Opened, the steps form a vertical list with an icon per
kind of work on a thin connector line, and a reasoning round shows its
summary under its title.

The shimmer and the dots are a `text-shimmer` utility and a reusable
WaitingText component, both still under reduced motion.

The demo's write block now carries `meta.errorCode: "demo.readOnly"`,
listed in the error-code catalogue, and the Coach answers it with an
honest line instead of the provider-outage copy.

Removes the interim preview component, the elapsed-seconds and summary
helpers, and their message keys in all seven locales.

docs/api/openapi.yaml

@@ -32867,7 +32867,7 @@ components:
                 cycle.bulk.too_large, cycle.calendar.invalid, cycle.calendar.range, cycle.cycles.invalid,
                 cycle.day-log.conflict, cycle.day-log.invalid, cycle.disabled, cycle.period.invalid,
                 cycle.symptom.custom.invalid, cycle.symptom.custom.limit; cycle-prefs — cycle-prefs.body.invalid_json,
-                cycle-prefs.invalid; disable-coach — disable-coach.body.invalid_json; documents —
+                cycle-prefs.invalid; disable-coach — disable-coach.body.invalid_json; demo — demo.readOnly; documents —
                 documents.chat.conversationNotFound, documents.chat.invalid, documents.inbound.alreadyConfirmed,
                 documents.inbound.alreadyPartlyConfirmed, documents.inbound.budgetExceeded,
                 documents.inbound.decryptFailed, documents.inbound.encounterNotFound, documents.inbound.episodeNotFound,