Performance: prune long-lived caches, hoist regexes, idle chart redraws

Three low-risk optimizations that reduce CPU/memory footprint without
changing user-visible behavior:

1. Periodic cleanup of unbounded module-level Maps (24/7 stability):
   - debridLinkKeyCooldowns, debridLinkKeyCooldownDetails,
     debridLinkKeyRuntimeStatuses (debrid.ts)
   - megaDebridAccountCooldowns (debrid.ts)
   - allDebridHostInfoCache (download-manager.ts)
   - All pruned every 10 min via existing resetStaleRetryState() with a
     1h grace window for debugging
   - Without this, modules accumulated entries indefinitely over days
     of continuous server operation

2. Hoist regex literals in resolveArchiveItemsFromList() to module scope.
   Avoids 5 RegExp constructions per call. The function is called per
   archive set during extraction discovery — adds up on packages with
   many archives.

3. BandwidthChart: skip the 250ms redraw interval while the session is
   stopped or paused. The chart renders once on state change to show the
   latest history, then sleeps until downloads resume. Saves 4 canvas
   redraws per second when idle (renderer CPU).

No functional changes. All 565 tests green.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/renderer/App.tsx

@@ -1325,11 +1325,20 @@ const BandwidthChart = memo(function BandwidthChart({ items, running, paused, sp
   }, [running, paused]);
 
   useEffect(() => {
+    // Always draw once on mount / when running/paused state changes so the
+    // chart shows the latest history.
+    drawChart();
+    // Only schedule periodic redraws while actively downloading — when
+    // stopped or paused the speed history doesn't change, so polling
+    // every 250ms would just burn CPU on the renderer process.
+    if (!running || paused) {
+      return;
+    }
     const interval = setInterval(() => {
       drawChart();
     }, 250);
     return () => clearInterval(interval);
-  }, [drawChart]);
+  }, [drawChart, running, paused]);
 
   useEffect(() => {
     // Only record samples while the session is running and not paused