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/chat.go

@@ -6,6 +6,8 @@ import (
 	"net/http"
 	"strings"
 
+	"github.com/a-h/templ"
+
 	"git.d-ma.be/mathias/tapir/internal/adapters/chat"
 	"git.d-ma.be/mathias/tapir/internal/adapters/store"
 )
@@ -43,6 +45,28 @@ type chatView struct {
 	History   []chat.Turn
 	Truncated bool
 	Error     string
+	// PostURL and Subject let the same chat panel serve an UPLOADED recording
+	// (ADR-033): where the form posts, and what the transcript is called. Empty
+	// means a YouTube video (/v/{VideoID}/chat, "video"), so existing callers are
+	// unchanged.
+	PostURL templ.SafeURL
+	Subject string
+}
+
+// postURL is where the chat form posts.
+func (v chatView) postURL() templ.SafeURL {
+	if v.PostURL != "" {
+		return v.PostURL
+	}
+	return chatURL(v.VideoID)
+}
+
+// subject is what the transcript is called in the panel's wording.
+func (v chatView) subject() string {
+	if v.Subject != "" {
+		return v.Subject
+	}
+	return "video"
 }
 
 // handleChat renders the chat page for a summarized video (GET). Entry is scoped