fix(ui-map): repaint fog as layered overpaint; rename to visibleHyperspace

The Phase 29 fog overlay rendered as a handful of random arc
segments instead of a clean union of holes around LOCAL planets
— Pixi v8's `Graphics.cut()` does not reliably subtract multiple
overlapping circles from a base path.

Replaced the cut-based approach with a layered overpaint: a
fog-tinted rectangle fills the world, then opaque background-
coloured circles are painted on top for every visibility circle.
The natural rendering order unions overlapping circles for free —
no geometry, no `cut()` quirks, one extra fill per circle.

Renamed the toggle from `visibilityFog` to `visibleHyperspace`
across the store, i18n strings, popover, tests, and docs. The
overlay still implements the visual "fog" effect at the renderer
level (FOG_COLOR, setVisibilityFog, getMapFog); the toggle is
named after the player-facing concept it controls — the portion
of the map that is visible (intelligence/scan coverage) — rather
than the obscured part.

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

ui/frontend/src/lib/active-view/map-toggles.svelte

@@ -185,11 +185,11 @@ bottom-tabs bar.
 				<label>
 					<input
 						type="checkbox"
-						data-testid="map-toggles-visibility-fog"
-						checked={store.mapToggles.visibilityFog}
-						onchange={(e) => setFlag("visibilityFog", e)}
+						data-testid="map-toggles-visible-hyperspace"
+						checked={store.mapToggles.visibleHyperspace}
+						onchange={(e) => setFlag("visibleHyperspace", e)}
 					/>
-					<span>{i18n.t("game.map.toggles.visibility_fog")}</span>
+					<span>{i18n.t("game.map.toggles.visible_hyperspace")}</span>
 				</label>
 				<div class="wrap-row">
 					<span class="wrap-label">{i18n.t("game.map.toggles.wrap.label")}</span>