Add Basic group alliance preview to lobby

components/game-table.tsx

@@ -2131,6 +2131,9 @@ export function GameTable({
           {g.status === 'playing' && g.shortAllianceVictory && <p className="notice">
             Optional alliance rule: a two-member alliance wins with three strongholds when at least three people or AI controllers are playing. Two-controller games retain their four-stronghold target.
           </p>}
+          {(g.status === 'playing' || g.status === 'setup') && g.coalitionPreview !== 'off' && <p className="notice">
+            Group alliances are an unfinished preview. Some faction powers and interactions are incomplete; this game does not certify the full optional rules.
+          </p>}
           {g.status === 'playing' && <MixedTraitorPromises game={g} />}
           {g.status === 'playing' && <TravelPromises game={g} busy={busy} act={act} />}
           {g.status === 'playing' && <TurnActionPromises game={g} busy={g.semutaReaction &&
@@ -2280,6 +2283,18 @@ export function GameTable({
                   onChange={(e) => act({type: 'shortAllianceVictory', enabled: e.target.checked})} />
                 Optional: two-member alliances win with three strongholds (three or more controllers)
               </label>
+              <label>Group alliances · unfinished preview
+                <select value={g.coalitionPreview} disabled={busy || g.host !== me.id}
+                  onChange={(e) => act({ type: 'coalitionPreview', variant: e.target.value })}>
+                  <option value="off">Off</option>
+                  <option value="three">Up to three members · four strongholds</option>
+                  <option value="three-short">Up to three members · three strongholds</option>
+                  <option value="unlimited">Unlimited members · three strongholds</option>
+                </select>
+              </label>
+              {g.coalitionPreview !== 'off' && <p className="notice">
+                This incomplete preview needs three to six classic factions in Basic rules, without expansion decks, other optional modules, two-person setup or the separate short-alliance setting. Some powers and interactions remain unfinished. Changing the selection clears human readiness.
+              </p>}
               <label className="checkbox-row">
                 <input
                   type="checkbox"