fix(insights): keep the assessment card polling while a stale text revalidates

The stale-while-revalidate path serves the last-good assessment on a cache
miss and returns a terminal payload, so the status hook stopped polling. The
worker warmed a fresh assessment out of band seconds later, but the open card
never picked it up — the stale text stuck until the page remounted.

Add a `revalidating` flag to the read-only miss outcome, set only when
last-good text is served AND a refresh was enqueued (false on the
suppressed-stub branch and when no prior text exists). Thread it through the
generic metric-status generator and the seven specialised generators onto the
wire, type it on the client, and make `nextStatusPollInterval` keep polling on
`preparing || revalidating`. The existing 12-attempt ceiling bounds both
signals, so a persistently failing generation still cannot poll forever.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
(cherry picked from commit c9217534fbdb304c4df1b6eb55fb19e4360b8a10)

docs/api/openapi.yaml

@@ -6559,6 +6559,11 @@ components:
           description: True when a first assessment is being generated out of band and no prior text exists yet — the client polls
             until it lands.
           type: boolean
+        revalidating:
+          description: True when `text` is served from last-good cache (stale-while-revalidate) while a fresh generation is in
+            flight. The payload is otherwise terminal; the client keeps polling on `preparing || revalidating` (bounded)
+            so the open card upgrades to the warmed assessment without a remount.
+          type: boolean
         insufficient:
           description: True when the metric has no readings; no assessment is generated (no LLM call). The card shows its
             insufficient-data state.