feat: enforce 2000 character limit on input

Add max_length=2000 to the input textbox so the displayed limit
is enforced client-side, not just shown as a soft indicator.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app.py

@@ -117,6 +117,7 @@ def _build_demo() -> gr.Blocks:
                 )
                 input_text = gr.Textbox(
                     lines=6,
+                    max_length=2000,
                     show_label=False,
                     buttons=["clear"],
                     info=_format_info(0),

tests/test_app.py

@@ -137,6 +137,13 @@ def test_input_textbox_height(demo):
     assert interactive[0].lines == 6, f"Expected lines=6, got {interactive[0].lines}"
 
 
+def test_input_textbox_max_length(demo):
+    """Input textbox should enforce 2000 character limit."""
+    textboxes = [b for b in demo.blocks.values() if type(b).__name__ == "Textbox"]
+    interactive = [t for t in textboxes if t.interactive is not False]
+    assert interactive[0].max_length == 2000, f"Expected max_length=2000, got {interactive[0].max_length}"
+
+
 def test_input_textbox_has_no_placeholder(demo):
     """Input textbox should have no placeholder text."""
     textboxes = [b for b in demo.blocks.values() if type(b).__name__ == "Textbox"]