fix: break import cycles

import/no-cycle (now active) flagged 17 cycles across 12 files:

- shared/ui self-barrel cycles (Logo/Stat/StatGroup/ComboControl/
  FilterGroup/SectionHeader): import siblings relatively instead of
  through the $shared/ui barrel that re-exports them
- shared/lib/utils: roundToStepPrecision imports getDecimalPlaces
  relatively instead of via the utils barrel
- routes: lazy-load Redirect in the router so it no longer statically
  imports a component that imports navigate back from it

src/routes/router.ts

@@ -1,6 +1,5 @@
 import { createRouter } from 'sv-router';
 import Home from './Home.svelte';
-import Redirect from './Redirect.svelte';
 
 /**
  * Single-page router for glyphdiff.
@@ -18,6 +17,8 @@ export const {
     '/': Home,
     /**
      * Any unmatched path redirects to home until additional routes exist.
+     * Lazy-loaded so `router` doesn't statically import `Redirect`, which
+     * imports `navigate` from here — breaks the import cycle.
      */
-    '*notfound': Redirect,
+    '*notfound': () => import('./Redirect.svelte'),
 });