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/tests/helpers/empty-ship-groups.ts

@@ -0,0 +1,27 @@
+// EMPTY_SHIP_GROUPS supplies empty arrays for the five ship-group /
+// fleet fields added to GameReport in Phase 19. Test fixtures spread
+// it into their report objects so the fixture body still focuses on
+// the fields under test, without forcing every spec to enumerate
+// the full GameReport surface.
+
+import type {
+	ReportIncomingShipGroup,
+	ReportLocalFleet,
+	ReportLocalShipGroup,
+	ReportOtherShipGroup,
+	ReportUnidentifiedShipGroup,
+} from "../../src/api/game-state";
+
+export const EMPTY_SHIP_GROUPS: {
+	localShipGroups: ReportLocalShipGroup[];
+	otherShipGroups: ReportOtherShipGroup[];
+	incomingShipGroups: ReportIncomingShipGroup[];
+	unidentifiedShipGroups: ReportUnidentifiedShipGroup[];
+	localFleets: ReportLocalFleet[];
+} = {
+	localShipGroups: [],
+	otherShipGroups: [],
+	incomingShipGroups: [],
+	unidentifiedShipGroups: [],
+	localFleets: [],
+};