feat(web): Processor port + in-flight ProcessingSet on App

Add the seam for immediate web-triggered summarization. Processor is the
optional single-video summarize port (nil = queue-only, unchanged behaviour);
ProcessingSet is an ephemeral, concurrency-safe set of in-flight (user,video)
ids so a status endpoint can show progress until the summary lands. State is
deliberately in-memory only — the DB holds the durable truth across restarts.

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

internal/web/handlers.go

@@ -61,6 +61,13 @@ type App struct {
 	// Secrets removes a user's OAuth tokens on disconnect / delete-account. The
 	// account routes require it; cmd/tapir wires the file-backed store.
 	Secrets SecretRemover
+	// Processor, when non-nil, summarizes a queued video immediately in a
+	// background goroutine (the "Summarize" button kicks it off). Nil = queue-only:
+	// the button flips the DB flag and the next `tapir run` does the work.
+	Processor Processor
+	// Processing tracks in-flight immediate summarizations so the status endpoint
+	// shows the animation until the summary lands. The zero value is ready to use.
+	Processing ProcessingSet
 }
 
 func (a *App) logger() *slog.Logger {