feat(web): chat with an uploaded transcript, reusing the ADR-027 path (ADR-033)

GET/POST /uploads/{id}/chat, mounted only when both an Uploader and a Chatter
are wired. The row comes from the user-scoped private store, so another user's
upload is a 404 before any model is involved. The owner's transcript goes to
the SAME Chatter with App.UploadChatMaxChars instead of the 18,000-char caption
default. The chat panel is shared, not forked: chatView gains PostURL/Subject
(empty = a YouTube video, so existing callers are unchanged). The done card
links to chat only when chat is wired.

Mutation-checked: dropping the upload budget, ignoring the done-status guard,
or scoping the lookup to the wrong user each turn tests red.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/web/handlers.go

@@ -113,6 +113,10 @@ type App struct {
 	// front rather than discovered by failing.
 	Uploads      Uploader
 	UploadLimits uploads.Limits
+	// UploadChatMaxChars is the transcript budget for chat over an uploaded
+	// recording. The caption default (18,000 chars, ~22 minutes of speech) would
+	// keep only the first third of an hour-long meeting.
+	UploadChatMaxChars int
 	// 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
@@ -186,6 +190,12 @@ func (a *App) Router() http.Handler {
 		app.HandleFunc("POST /uploads", a.handleUploadPost)
 		app.HandleFunc("GET /uploads/{id}", a.handleUploadDetail)
 		app.HandleFunc("GET /uploads/{id}/status", a.handleUploadStatus)
+		// Chat over the uploaded transcript reuses the ADR-027 Chatter; mounted only
+		// when one is wired.
+		if a.Chat != nil {
+			app.HandleFunc("GET /uploads/{id}/chat", a.handleUploadChat)
+			app.HandleFunc("POST /uploads/{id}/chat", a.handleUploadChatMessage)
+		}
 	}
 	app.HandleFunc("GET /register", a.handleRegisterForm)
 	app.HandleFunc("POST /register", a.handleRegister)