fix(ui-calculator): keep calculator state long-lived; don't eject on planet click

Move the calculator's inputs into a page-level calculatorState singleton so they survive the sidebar unmounting the tab on a tab switch (the inspector auto-opens on a planet click). ensureGame resets the design when the active game changes.

While on the calculator, a planet click no longer switches to the inspector — the calculator consumes the selection in its planet area / reach circles. Halve the reach-circle stroke width.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ui/frontend/src/routes/games/[id]/+layout.svelte

@@ -43,7 +43,7 @@ the next game's snapshot — and the next game's selection — start
 fresh.
 -->
 <script lang="ts">
-	import { onDestroy, onMount, setContext } from "svelte";
+	import { onDestroy, onMount, setContext, untrack } from "svelte";
 	import { goto } from "$app/navigation";
 	import { page } from "$app/state";
 	import Header from "$lib/header/header.svelte";
@@ -223,7 +223,17 @@ fresh.
 	$effect(() => {
 		const sel = selection.selected;
 		if (sel === null) return;
-		activeTab = "inspector";
+		// Stay in the calculator when a planet is picked: the calculator
+		// consumes the selection in its planet area + reach circles, and
+		// it is a long-lived workspace the user should not be ejected
+		// from. `activeTab` is read untracked so a manual tab switch does
+		// not re-fire this effect. Any other case (including a ship-group
+		// selection, which the calculator does not use) reveals the
+		// inspector as before.
+		const tab = untrack(() => activeTab);
+		if (!(tab === "calculator" && sel.kind === "planet")) {
+			activeTab = "inspector";
+		}
 		sidebarOpen = true;
 	});