ui/phase-19: ship-group decoder + map binding + selection store

Wires Phase 19's data and rendering layers without yet adding the
inspector UI:

  - game-state.ts grows ReportLocalShipGroup / ReportOtherShipGroup
    / ReportIncomingShipGroup / ReportUnidentifiedShipGroup /
    ReportLocalFleet types and walks the matching FlatBuffers
    vectors (LocalGroup, OtherGroup, IncomingGroup,
    UnidentifiedGroup, LocalFleet) inside decodeReport. The Tech
    map is folded into the fixed-shape ShipGroupTech struct;
    cargo strings normalise to the closed CargoLoadType | "NONE"
    union; UUIDs come back as canonical 36-char strings.
  - synthetic-report.ts mirrors the new fields so the DEV-only
    lobby loader can feed JSON produced by legacy-report-to-json
    straight into the live UI surface.
  - selection.svelte.ts widens its discriminated union with a
    `kind: "shipGroup"` branch carrying a ShipGroupRef
    (local UUID / other / incoming / unidentified by index).
  - world.ts adds Style.strokeDashPx and render.ts.drawLine
    honours it via manual segmentation (PixiJS v8 has no native
    dash API). Ignored on points and circles.
  - state-binding.ts now returns { world, hitLookup }: the
    hit-lookup map keys every primitive id back to a concrete
    HitTarget so the click handler can dispatch to selectPlanet
    or selectShipGroup. Ship-group primitives live in a separate
    ship-groups.ts that emits one point per local / other /
    unidentified group, plus a dashed origin→destination line +
    clickable point per incoming group. Position is interpolated
    along the trajectory for in-hyperspace groups.
  - map.svelte threads the hitLookup into handleMapClick.

Vitest:
  - tests/helpers/empty-ship-groups.ts exposes EMPTY_SHIP_GROUPS
    so existing fixtures can spread the new five empty arrays
    without enumerating every field.
  - state-binding-groups.test.ts covers each group variant's
    primitive geometry and lookup correctness.
  - All previously-existing fixture builders pick up the spread
    so GameReport stays a complete object.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

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

@@ -28,7 +28,8 @@ preference the store already manages.
 		type RendererHandle,
 	} from "../../map/index";
 	import { buildCargoRouteLines } from "../../map/cargo-routes";
-	import { reportToWorld } from "../../map/state-binding";
+	import { reportToWorld, type HitTarget } from "../../map/state-binding";
+	import type { PrimitiveID } from "../../map/world";
 	import {
 		GAME_STATE_CONTEXT_KEY,
 		type GameStateStore,
@@ -76,6 +77,7 @@ preference the store already manages.
 	let mountError: string | null = $state(null);
 
 	let handle: RendererHandle | null = null;
+	let hitLookup = new Map<PrimitiveID, HitTarget>();
 	let mountedTurn: number | null = null;
 	let mountedGameId: string | null = null;
 	let onResize: (() => void) | null = null;
@@ -213,7 +215,8 @@ preference the store already manages.
 			handle = null;
 		}
 		try {
-			const world = reportToWorld(report);
+			const { world, hitLookup: nextHitLookup } = reportToWorld(report);
+			hitLookup = nextHitLookup;
 			handle = await createRenderer({
 				canvas: canvasEl,
 				world,
@@ -339,11 +342,14 @@ preference the store already manages.
 		}
 	}
 
-	// handleMapClick translates a renderer click into a planet
-	// selection. A click that misses every primitive (empty space) is
-	// a deliberate no-op: the selection rule for Phase 13 is that
-	// only the explicit close button on the mobile sheet clears the
-	// current selection.
+	// handleMapClick translates a renderer click into a selection
+	// update. A click that misses every primitive (empty space) is a
+	// deliberate no-op: the selection rule from Phase 13 is that only
+	// the explicit close button on the mobile sheet clears the
+	// current selection. The Phase 19 ship-group surface dispatches
+	// through the same `hit-test` plumbing — the hitLookup map keyed
+	// by primitive id resolves a hit back to either a planet or a
+	// ship-group selection variant.
 	function handleMapClick(cursorPx: { x: number; y: number }): void {
 		if (handle === null || store?.report === undefined || store.report === null) {
 			return;
@@ -352,10 +358,13 @@ preference the store already manages.
 		const hit = handle.hitAt(cursorPx);
 		if (hit === null) return;
 		if (hit.primitive.kind !== "point") return;
-		const planetId = hit.primitive.id;
-		const planet = store.report.planets.find((p) => p.number === planetId);
-		if (planet === undefined) return;
-		selection.selectPlanet(planet.number);
+		const target = hitLookup.get(hit.primitive.id);
+		if (target === undefined) return;
+		if (target.kind === "planet") {
+			selection.selectPlanet(target.number);
+		} else {
+			selection.selectShipGroup(target.ref);
+		}
 	}
 
 	onMount(() => {