Collectives P1: participation landing (ES/EN), group tree, room provisioning APIs

- 030: groups.parent_id tree + kind discriminator + group_rooms mapping
- /collectives module: create/tree/join APIs, MatrixProvisioner (open room
  public+federated, closed room E2EE-at-creation, onboarding room), NullProvisioner
  fail-soft when ARCHIVE_PROVISIONER_* unset
- web root becomes the public participation manual (ES-first + EN toggle,
  three paths: join by invite, start collective, solo account)
- participation manual content in core

apps/web/src/app/join/[token]/page.tsx

@@ -6,6 +6,7 @@ import { Badge, Button, Card, Input } from "../../../components/ui/primitives";
 import { LoadingPanel } from "../../../components/brand/loading";
 import { apiFetch, ApiError, ApiUnreachableError, errorMessage } from "../../../lib/api-client";
 import type { InviteInfo } from "../../../lib/api-types";
+import type { ManualLanguage } from "@tactical-media-broadcast-hub/core";
 import { useAuth } from "../../../lib/auth-store";
 
 const MIN_PASSWORD = 10;
@@ -29,6 +30,16 @@ function deadReasonFrom(err: unknown): DeadReason {
 
 const isAlreadyMember = (err: unknown): boolean => err instanceof ApiError && err.status === 409;
 
+/**
+ * One-line collective labelling for the claim card ("Collectives: X · Y").
+ * Null when unknown or empty — the card must read fine without it.
+ */
+function collectiveLabel(collectives: Array<{ id: string; name: string }> | null, lang: ManualLanguage): string | null {
+  if (collectives === null || collectives.length === 0) return null;
+  const names = collectives.map((c) => c.name).join(" · ");
+  return lang === "es" ? `Colectivos: ${names}` : `Collectives: ${names}`;
+}
+
 function usesLeftLine(info: InviteInfo): string {
   const left = info.maxUses === null ? "unlimited uses" : `${Math.max(info.maxUses - info.usedCount, 0)} use${info.maxUses - info.usedCount === 1 ? "" : "s"} left`;
   return `${left} · expires ${new Date(info.expiresAt).toLocaleDateString()}`;
@@ -183,6 +194,9 @@ export default function JoinWorkspacePage({ params }: { params: { token: string
   const [claimError, setClaimError] = useState<string | null>(null);
   const [alreadyMember, setAlreadyMember] = useState(false);
   const [attempt, setAttempt] = useState(0);
+  // Collective names for the claim card (names-only public read). Purely
+  // cosmetic labelling: a failure renders the card without it, never blocks.
+  const [collectives, setCollectives] = useState<Array<{ id: string; name: string }> | null>(null);
 
   // The preview is public: fetch it immediately rather than waiting for the session to settle.
   useEffect(() => {
@@ -193,6 +207,14 @@ export default function JoinWorkspacePage({ params }: { params: { token: string
         if (cancelled) return;
         setInfo(preview);
         setPhase("preview");
+        // Best-effort collective labelling: the token is already proven valid.
+        apiFetch<{ collectives: Array<{ id: string; name: string }> }>(`/collectives-public/for-invite/${encodeURIComponent(params.token)}`, {
+          redirectOn401: false,
+        })
+          .then((result) => {
+            if (!cancelled) setCollectives(result.collectives);
+          })
+          .catch(() => undefined);
       })
       .catch((err: unknown) => {
         if (cancelled) return;
@@ -288,6 +310,9 @@ export default function JoinWorkspacePage({ params }: { params: { token: string
           <Badge tone="accent">{info.role}</Badge>.
         </p>
         <p className="mt-2 text-2xs text-text-faint">{usesLeftLine(info)}</p>
+        {collectiveLabel(collectives, "en") !== null && (
+          <p className="mt-1 text-2xs text-text-faint">{collectiveLabel(collectives, "en")}</p>
+        )}
         {claimError !== null && <p className="mt-2 text-xs text-danger">{claimError}</p>}
         {memberCta}
       </Card>
@@ -309,6 +334,9 @@ export default function JoinWorkspacePage({ params }: { params: { token: string
         <p className="mt-1 text-2xs text-text-faint">
           You&apos;ve been invited as <Badge tone="accent">{info.role}</Badge> · {usesLeftLine(info)}
         </p>
+        {collectiveLabel(collectives, "en") !== null && (
+          <p className="mt-0.5 text-2xs text-text-faint">{collectiveLabel(collectives, "en")}</p>
+        )}
       </div>
       {mode === "signin" ? (
         <JoinSignInForm token={params.token} onSwitch={() => setMode("register")} onAlreadyMember={() => setAlreadyMember(true)} />