feat(web): WelcomePage landing component

Add the public landing page: a static Charm-box tapir mascot (reusing the
shared tapirLine helpers and charm palette), a tagline, and a single
'Get Started' CTA into the shared Dex flow — sign-in and sign-up are the
same URL (ADR-012). Logged-in visitors get a greeting plus links back into
the app and to log out. Regenerated views_templ.go committed alongside.

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

internal/web/views.templ

@@ -31,6 +31,40 @@ templ Layout(title string) {
 	</html>
 }
 
+// WelcomePage is the public landing page (served at /welcome, outside the auth
+// guard — ADR-012). Logged out: the tapir mascot, a one-line tagline, and a
+// single "Get Started" CTA into the shared Dex flow (sign-in and sign-up are the
+// same URL). Logged in: a greeting plus links back into the app and to log out.
+templ WelcomePage(user User, loggedIn bool) {
+	@Layout("Tapir — Watch less, know more") {
+		<section class="welcome">
+			<div class="welcome-hero">
+				<pre aria-hidden="true">@templ.Raw(welcomeHero)</pre>
+			</div>
+			if loggedIn {
+				<h1 class="welcome-title">Welcome back</h1>
+				if user.Email != "" {
+					<p class="welcome-tagline">Signed in as { user.Email }.</p>
+				}
+				<div class="welcome-cta">
+					<a class="btn btn-lg" href="/">Go to my Tapir</a>
+					<a class="btn-secondary" href="/auth/logout">Log Out</a>
+				</div>
+			} else {
+				<h1 class="welcome-title">Watch less, know more</h1>
+				<p class="welcome-tagline">
+					Tapir summarizes the videos your subscriptions publish, so you can
+					skim the gist and decide what is worth your time.
+				</p>
+				<div class="welcome-cta">
+					<a class="btn btn-lg" href="/auth/login">Get Started</a>
+				</div>
+				<p class="welcome-sub">Already have an account? You'll go straight through.</p>
+			}
+		</section>
+	}
+}
+
 // flashBanner renders a one-shot notification for a flash code (connect success/
 // failure, disconnect, delete, registration). An empty or unknown code renders
 // nothing, so it is safe to drop into any page unconditionally. Reused across the