feat(mining): fetch pool hashrates + miner version at startup

Warm the Mining tab's data during App::init() (both off the UI thread) instead of
only when the user opens the tab or clicks a mine / auto-balance button:
- kick the idempotent one-shot `xmrig --version` detection, and
- kick a background pool-stats refresh over the known pools.

Gated on supportsPoolMining(). The pool-stats snapshot lands on a later frame and
the auto-balance driver's self-throttling still applies, so this is just an
earlier first fetch — hashrates + version are visible as soon as the tab opens.

Full-node + lite build clean; ctest green; source hygiene clean.

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

src/app.cpp

@@ -396,6 +396,14 @@ bool App::init()
     worker_->start();
     network_refresh_.markDue(services::NetworkRefreshService::Timer::Price);
 
+    // Warm the Mining tab's data at startup (both async / off the UI thread) so pool
+    // hashrates and the installed miner version are shown as soon as the tab is opened,
+    // instead of only after the user clicks a mine / auto-balance button.
+    if (supportsPoolMining()) {
+        daemon::XmrigManager::startVersionDetection();   // idempotent one-shot `xmrig --version`
+        pool_stats_service_.refresh(util::knownPools());  // snapshot lands on a later frame
+    }
+
     // Forward error/warning notifications to the console tab. The channel is the semantic
     // key — the Errors filter keys off ConsoleChannel::Error, and the color/accent bar are
     // derived from the channel at draw time.