feat(app): font-atlas rebuild hook + clock/emoji sync

- requestFontRebuild() + preFrame handling so toggling color emoji swaps the atlas live;
  request a rebuild at startup when the saved setting wants color.
- preFrame syncs Typography's color-emoji flag and the util clock flag from settings.
- Chat 0-conf fast-scan cadence now reads the user's poll-rate setting (was a hardcoded 2.5s).

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

src/app.h

@@ -171,6 +171,9 @@ public:
     daemon::EmbeddedDaemon* consoleDaemon();
     daemon::XmrigManager* consoleXmrig();
     config::Settings* settings() { return settings_.get(); }
+    // Request a font-atlas rebuild before the next frame (e.g. after toggling color emoji). Handled in
+    // preFrame() via Typography::reload — safe to call from UI code mid-frame.
+    void requestFontRebuild() { font_rebuild_requested_ = true; }
     // Lite wallet controller (non-null only in lite builds with a linked backend).
     wallet::LiteWalletController* liteWallet() { return lite_wallet_.get(); }
     // HushChat service (identity + in-memory message store); the Chat tab reads its store.
@@ -736,6 +739,7 @@ private:
     void fastScanChatMemos();
     bool chat_fast_scan_in_flight_ = false;   // guard against overlapping fast-scan RPCs
     float chat_fast_scan_accum_ = 0.0f;       // seconds since the last fast-scan (dedicated ~2.5s poll)
+    bool font_rebuild_requested_ = false;     // set by requestFontRebuild(); consumed in preFrame()
     // Lite first-run welcome prompt: dismissed for the session once the user picks an action.
     bool lite_firstrun_dismissed_ = false;
     // Lite send-time unlock: set to show the unlock modal when a spend is attempted while locked.