feat(dashboard): poll optimisation — T4, T5, T6

T4: workstreams.md and dependencies.md now call /state/deps instead of the
    full /state/summary — removes 2 heavy 10-table queries per 60 s cycle.

T5: index.md's 4 independent polling loops (summaryState, sbomSnapState,
    regsState, wsChartState) consolidated into a single pageState generator
    with one Promise.all batch and a shared backoff counter.

T6: config.js gains waitForVisible(ms) — pauses polling entirely while the
    tab is hidden and fires immediately on visibilitychange.  pollDelay()
    simplified (hidden-tab POLL_HIDDEN logic removed).  All 16 polling pages
    migrated from await sleep(pollDelay(...)) to await waitForVisible(pollDelay(...)).

CUST-WP-0039 complete — all 6 tasks done.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

dashboard/src/progress.md

@@ -3,7 +3,7 @@ title: Progress
 ---
 
 ```js
-import {POLL_HEAVY, apiFetch, pollDelay, sleep} from "./components/config.js";
+import {POLL_HEAVY, apiFetch, pollDelay, waitForVisible} from "./components/config.js";
 ```
 
 ```js
@@ -22,7 +22,7 @@ const progState = (async function*() {
     } catch {}
     failures = ok ? 0 : failures + 1;
     yield {data, tokenEvents, ok, ts: new Date()};
-    await sleep(pollDelay({ok, base: POLL_HEAVY, failures}));
+    await waitForVisible(pollDelay({ok, base: POLL_HEAVY, failures}));
   }
 })();
 ```