ui/phase-19: read-only ship-group inspector + sheet + tab dispatch

Closes Phase 19's UI surface. The inspector dispatches on the
selection variant: local / other groups render class, count, the
four tech levels, mass, cargo (type + amount when loaded),
location (planet name on-orbit, from/to/distance in hyperspace),
and — for local groups only — fleet membership + state. Incoming
groups surface origin / destination / distance / speed and the
inline ETA = ceil(distance / speed); zero speed collapses to the
designer's existing "—" placeholder. Unidentified groups render
just the (x, y) coordinates and the no-data hint, mirroring the
unidentified planet treatment.

Layout / inspector-tab plumbing:
  - inspector-tab.svelte derives selectedShipGroup against the
    rendered report and mounts <ShipGroup /> when the planet
    branch doesn't match. Stale refs (an index that no longer
    resolves after a turn refresh) collapse cleanly to the empty
    state.
  - +layout.svelte mounts <ShipGroupSheet /> alongside the
    existing planet sheet on mobile; both share the
    `effectiveTool === "map"` guard and clear-on-close.

i18n: en + ru both grow ~30 keys under
`game.inspector.ship_group.*`. Adding a key to one without the
other is a TS error (TranslationKey is `keyof typeof en`), so the
Russian mirror stays mandatory.

Tests:
  - inspector-ship-group.test.ts exercises every variant —
    on-planet local, in-hyperspace local, cargo-loaded local,
    foreign, incoming with ETA, incoming with zero speed,
    unidentified, plus the missing-planet `#NN` fallback.
  - tests/e2e/inspector-ship-group.spec.ts is a smoke spec that
    drives the DEV-only synthetic-report loader from /lobby
    through navigation to /games/synthetic-XXX/map.

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

ui/frontend/src/lib/sidebar/inspector-tab.svelte

@@ -7,6 +7,12 @@ only planet inspector. A selection that points at a planet missing
 from the current report (e.g. visibility lost between turns) falls
 back to the empty state instead of holding stale data.
 
+Phase 19 widens the dispatch: a `kind === "shipGroup"` selection
+resolves against the matching report array and mounts the read-only
+ship-group inspector. Unresolvable refs (e.g. the chosen index has
+fallen out of the new turn's report) cleanly collapse to the empty
+state — same fallback as a stale planet selection.
+
 The empty-state copy still matches the IA section verbatim — `select
 an object on the map` — so the no-selection experience is unchanged
 from the Phase 10 stub.
@@ -23,6 +29,9 @@ from the Phase 10 stub.
 		type RenderedReportSource,
 	} from "$lib/rendered-report.svelte";
 	import Planet from "$lib/inspectors/planet.svelte";
+	import ShipGroup, {
+		type ShipGroupSelection,
+	} from "$lib/inspectors/ship-group.svelte";
 
 	const renderedReport = getContext<RenderedReportSource | undefined>(
 		RENDERED_REPORT_CONTEXT_KEY,
@@ -38,6 +47,38 @@ from the Phase 10 stub.
 		if (report === undefined || report === null) return null;
 		return report.planets.find((p) => p.number === sel.id) ?? null;
 	});
+	const selectedShipGroup: ShipGroupSelection | null = $derived.by(() => {
+		const sel = selection?.selected;
+		if (sel === undefined || sel === null || sel.kind !== "shipGroup") {
+			return null;
+		}
+		const report = renderedReport?.report;
+		if (report === undefined || report === null) return null;
+		const ref = sel.ref;
+		switch (ref.variant) {
+			case "local": {
+				const group = report.localShipGroups.find((g) => g.id === ref.id);
+				if (group === undefined) return null;
+				return { variant: "local", group };
+			}
+			case "other": {
+				const group = report.otherShipGroups[ref.index];
+				if (group === undefined) return null;
+				return { variant: "other", group };
+			}
+			case "incoming": {
+				const group = report.incomingShipGroups[ref.index];
+				if (group === undefined) return null;
+				return { variant: "incoming", group };
+			}
+			case "unidentified": {
+				const group = report.unidentifiedShipGroups[ref.index];
+				if (group === undefined) return null;
+				return { variant: "unidentified", group };
+			}
+		}
+	});
+
 	const localShipClass = $derived(
 		renderedReport?.report?.localShipClass ?? [],
 	);
@@ -61,6 +102,8 @@ from the Phase 10 stub.
 			{mapHeight}
 			{localPlayerDrive}
 		/>
+	{:else if selectedShipGroup !== null}
+		<ShipGroup selection={selectedShipGroup} planets={allPlanets} />
 	{:else}
 		<h3>{i18n.t("game.sidebar.tab.inspector")}</h3>
 		<p>{i18n.t("game.sidebar.empty.inspector")}</p>