feat(web): immediate summarize + status poll + ASCII tapir spinner

Clicking "Summarize" now runs the summary in the background (when a Processor is
wired) instead of only queuing it. The handler flips the DB flag, kicks off the
work on a detached context, and returns an animated "processing" card that polls
GET /v/{id}/status every 2s via HTMX. Status returns the summary card once it
lands (no poll → polling stops), the animation while in-flight, or the Queued
card otherwise. Queue-only behaviour is unchanged when no Processor is set.

The spinner is a CSS-only cross-fade of three ASCII tapir frames — no JS, honours
prefers-reduced-motion.

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

internal/web/handlers.go

@@ -91,6 +91,7 @@ func (a *App) Router() http.Handler {
 	app.HandleFunc("GET /v/{videoId}", a.handleDetail)
 	app.HandleFunc("POST /v/{videoId}/action", a.handleAction)
 	app.HandleFunc("POST /v/{videoId}/summarize", a.handleRequestSummarize)
+	app.HandleFunc("GET /v/{videoId}/status", a.handleStatus)
 	app.HandleFunc("GET /register", a.handleRegisterForm)
 	app.HandleFunc("POST /register", a.handleRegister)
 
@@ -215,10 +216,12 @@ func (a *App) handleAction(w http.ResponseWriter, r *http.Request) {
 	http.Redirect(w, r, "/v/"+videoID, http.StatusSeeOther)
 }
 
-// handleRequestSummarize queues a video for manual summarization. It does NOT run
-// the engine inline — it only flips summarize_requested; the next `tapir run`
-// picks it up (the single summarization driver). For HTMX it returns the refreshed
-// card (now showing "Queued"); without JS it redirects back to the list.
+// handleRequestSummarize handles the "Summarize" button. It always flips the DB
+// flag (summarize_requested) so the work is durable. With a Processor wired it
+// then summarizes immediately in the background and answers with the animated
+// processing card that polls /status until done; without one (queue-only) it
+// answers with the "Queued" card — the next `tapir run` does the work. Without
+// JS it redirects back to the list (POST→redirect→GET).
 func (a *App) handleRequestSummarize(w http.ResponseWriter, r *http.Request) {
 	userID, ok := a.currentUserID(w, r)
 	if !ok {
@@ -245,9 +248,60 @@ func (a *App) handleRequestSummarize(w http.ResponseWriter, r *http.Request) {
 		a.serverError(w, r, "get video", err)
 		return
 	}
+
+	if a.Processor != nil {
+		a.startProcessing(userID, videoID)
+		a.render(w, r, processingCard(*row))
+		return
+	}
 	a.render(w, r, VideoCard(*row))
 }
 
+// startProcessing marks a video in-flight and summarizes it in the background.
+// The goroutine uses a detached context — not the request's, which is cancelled
+// when the handler returns — and clears the in-flight mark on completion. On
+// error the DB flag stays set, so the video remains queued for the next
+// `tapir run`; a successful Processor.ProcessVideo clears it itself.
+func (a *App) startProcessing(userID, videoID string) {
+	key := processingKey(userID, videoID)
+	a.Processing.Add(key)
+	go func() {
+		defer a.Processing.Remove(key)
+		if err := a.Processor.ProcessVideo(context.Background(), userID, videoID); err != nil {
+			a.logger().Error("background summarize", "user", userID, "video", videoID, "err", err)
+		}
+	}()
+}
+
+// handleStatus is the HTMX poll target for an in-flight summarization. It returns
+// the card in its current state: the full summary card once the summary exists,
+// otherwise the animated processing card while still in-flight (which keeps
+// polling), or the queued/button card when neither holds. VideoCard carries no
+// polling attributes, so HTMX stops polling once it swaps in.
+func (a *App) handleStatus(w http.ResponseWriter, r *http.Request) {
+	userID, ok := a.currentUserID(w, r)
+	if !ok {
+		return
+	}
+	videoID := r.PathValue("videoId")
+
+	row, err := a.Store.GetVideoRow(r.Context(), userID, videoID)
+	if errors.Is(err, store.ErrNotFound) {
+		http.NotFound(w, r)
+		return
+	}
+	if err != nil {
+		a.serverError(w, r, "get video", err)
+		return
+	}
+
+	if row.Summarized || !a.Processing.Has(processingKey(userID, videoID)) {
+		a.render(w, r, VideoCard(*row))
+		return
+	}
+	a.render(w, r, processingCard(*row))
+}
+
 // handleSummarizeMode toggles the user's auto/manual summarization mode. The form
 // submits the desired new value (enabled=true|false). For HTMX it returns the
 // refreshed mode control; without JS it redirects back to the account page.