fix(web): correct stale welcome-page invite copy

The landing page promised "if you have an invite link, it will set up your
account automatically" — but invites moved to Authentik (ADR-019); Tapir no
longer handles invite links and "Get Started" goes straight to OIDC. Replace
with honest "invite-only — if you've been invited, sign in" and set the
gradual-fill expectation before the login wall (UX review A5). Test pins the
stale phrase out.

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

internal/web/views.templ

@@ -84,7 +84,7 @@ templ WelcomePage(user User, loggedIn bool) {
 				<div class="welcome-cta">
 					<a class="btn btn-lg" href="/auth/login">Get Started</a>
 				</div>
-				<p class="welcome-sub">Access is by invitation. If you have an invite link, it will set up your account automatically. Returning users with credentials can log in above.</p>
+				<p class="welcome-sub">Tapir is invite-only right now. If you've been invited, sign in above. New summaries land gradually — Tapir fetches captions slowly to respect YouTube's limits.</p>
 			}
 		</section>
 	}