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)

src/lib/openapi/routes.ts

@@ -1144,6 +1144,12 @@ const metricStatusResponse = z
       .describe(
         "True when a first assessment is being generated out of band and no prior text exists yet — the client polls until it lands.",
       ),
+    revalidating: z
+      .boolean()
+      .optional()
+      .describe(
+        "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.",
+      ),
     insufficient: z
       .boolean()
       .optional()