test(web): match the HTML-escaped tail of the inline chat error

templ escapes the apostrophe in "couldn't", so the assertion could never match
the rendered page. A test defect, not a loosening: the failure must still be
shown inline with the conversation kept.

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

internal/web/uploads_chat_handler_test.go

@@ -145,7 +145,7 @@ func TestUploadChatPost_AModelFailureIsShownInlineNotAs500(t *testing.T) {
 
 	require.Equal(t, http.StatusOK, rec.Code)
 	b := body(t, rec)
-	assert.Contains(t, b, "couldn't answer")
+	assert.Contains(t, b, "answer just now", "the failure is inline (the apostrophe is HTML-escaped, so match the tail)")
 	assert.Contains(t, b, "kept", "the conversation survives a failed turn")
 }