fix(ai): extract reindex-button loading predicate + correct poll comment (PR #242)

F4: extract the reindex button `loading` predicate into a pure, unit-tested
`isReindexButtonLoading({ mutationPending, deadline, status })` next to the
other reindex helpers, replacing the inline JSX expression. Covers the
load-bearing post-cap case (deadline nulled, reindexing stale-true -> not
loading) plus mutationPending, active-run, and finished cases.

F5: rewrite the `useAiSettingsQuery` poll comment to match the actual
`nextReindexPollInterval` stop condition (continues while reindexing===true OR
within deadline and not fully indexed; stops only when reindexing===false &&
indexed>=total, or the deadline cap) instead of the stale "until indexed===total".

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

apps/client/src/features/workspace/queries/ai-settings-query.ts

@@ -23,8 +23,12 @@ export function useAiSettingsQuery(
   enabled: boolean = true,
   // While reindexing runs as an async background job, the counter only climbs
   // if the client keeps refetching. The component passes a refetchInterval
-  // function that polls until indexed === total or a bounded deadline, then
-  // returns false to stop. See AiProviderSettings.
+  // function (`nextReindexPollInterval`) that keeps polling while the server
+  // reports an active run (reindexing === true) OR we are still within the
+  // bounded deadline and not yet fully indexed; it returns false to stop only
+  // once the run has finished AND indexed >= total, or the deadline cap is hit
+  // (the cap always wins). Note: a transient indexed === total during an active
+  // run does NOT stop polling. See AiProviderSettings.
   refetchInterval?:
     | number
     | false