ui: fix hero heading grammar; default Max Turns 6 -> 15

- "What I can research for you?" -> "What can I search for you?"
- Max Turns slider default value 6 -> 15 (research questions typically need
~10-15 turns to converge; 6 was too low and many runs hit the cap)

app.py

@@ -2386,7 +2386,7 @@ with gr.Blocks(
             with gr.Group(elem_classes="section-card"):
                 gr.HTML(
                     '<div class="section-heading">Ask the agent</div>'
-                    '<div class="hero-heading"><span class="quest-name">QUEST</span>: What I can research for you?</div>'
+                    '<div class="hero-heading"><span class="quest-name">QUEST</span>: What can I search for you?</div>'
                 )
                 question = gr.Textbox(
                     show_label=False,
@@ -2485,7 +2485,7 @@ with gr.Blocks(
                     label="Max Turns",
                     minimum=2,
                     maximum=50,
-                    value=6,
+                    value=15,
                     step=1,
                     elem_id="quest-max-turns",
                 )