§22 S4: release v0.43.0 — invitation surfaces + role-aware empty states (@S4)

Bump VERSION + frontend/package.json to 0.43.0, add the CHANGELOG entry
(minor, non-breaking — additive endpoints + UI, no migration, no change to
existing authz outcomes), and mark Part E slice S4 shipped in the design doc.

Completes @S4 (C2.1–C2.7 invitation + C3.3–C3.5 role-aware empty states).
Next: S5 (in-app create-project + the global directory, C3.1–C3.2).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/design/2026-06-05-three-tier-projects-collections.md

@@ -581,13 +581,17 @@ means the deployment runs and either gains a capability or provably loses none
   hidden from the public. **Completes:** `@S3` (all of C.1 — role usage,
   inheritance, union, no-negative-override).
 
-- **S4 — Invitation surfaces + role-aware empty states.** The invite UI
+- **S4 — Invitation surfaces + role-aware empty states.** *(Shipped v0.43.0.)*
+  The invite UI
   (Owner-only) granting Owner/RFC Contributor at a scope or any scope beneath it,
   with §15 notifications and the broader-scope-supersedes rule; the
   create-first-collection / propose-first empty states keyed to the actor's role.
-  **Usable end-state:** an Owner invites collaborators at the right scope from
-  the UI. **Completes:** `@S4` (all of C.2 — invitation; plus the project/
-  collection empty states C3.3–C3.5).
+  Modelled as a **direct grant** to an existing account looked up by email (the
+  C.2 scenarios write the membership row immediately and §15-notify an existing
+  user — no accept round-trip; inviting a not-yet-account email is out of S4
+  scope, handled by the admin-create-invite path). **Usable end-state:** an Owner
+  invites collaborators at the right scope from the UI. **Completes:** `@S4` (all
+  of C.2 — invitation; plus the project/collection empty states C3.3–C3.5).
 
 - **S5 — In-app create-project + the global directory.** The global-Owner
   **create-project** action (bot provisions a Gitea content repo + commits to