feat(domain): add SourceRateLimited transcript source

429 from the caption endpoint means the IP is rate-limited (retry later),
not that the video has no captions. Distinguishing it from SourceNone is the
prerequisite for the runner's backoff/retry logic.

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

internal/web/views.templ

@@ -79,12 +79,12 @@ templ flashBanner(code string) {
 // #summary-list region; a non-HTMX request renders the whole page. flash carries
 // a one-shot notification (e.g. "connected", "registered") surfaced on arrival
 // after a POST→redirect.
-templ ListPage(rows []store.SummaryRow, f Filter, flash string) {
+templ ListPage(rows []store.SummaryRow, f Filter, flash string, hasConnected bool) {
 	@Layout("Tapir — Summaries") {
 		@flashBanner(flash)
 		@filterForm(f)
 		<div id="summary-list">
-			@summaryList(rows)
+			@summaryList(rows, hasConnected)
 		</div>
 	}
 }
@@ -110,12 +110,20 @@ templ filterForm(f Filter) {
 // summaryList is the swappable list fragment: one card per video (summarized or
 // not). Cards reflow to a single column on mobile; an empty list shows a friendly
 // first-run state instead of a blank table.
-templ summaryList(rows []store.SummaryRow) {
+templ summaryList(rows []store.SummaryRow, hasConnected bool) {
 	if len(rows) == 0 {
-		<div class="empty">
-			<strong>No videos yet</strong>
-			<span>Videos appear here as your subscriptions are processed — run <code>tapir run</code> to fetch them. In manual mode, use the Summarize button to queue one.</span>
-		</div>
+		if hasConnected {
+			<div class="empty empty-connected">
+				<strong>Your YouTube account is connected!</strong>
+				<span>Run <code>tapir run</code> to discover your subscriptions. Videos will appear here once discovered. In manual mode, each new video gets a Summarize button.</span>
+			</div>
+		} else {
+			<div class="empty">
+				<strong>No videos yet</strong>
+				<span>Connect your YouTube account to get started.</span>
+				<p><a class="btn" href="/oauth/youtube/connect">Connect YouTube</a></p>
+			</div>
+		}
 	} else {
 		<ul class="cards">
 			for _, r := range rows {