feat: enable up/down arrow history navigation in CLI

The TextArea uses multiline=True, so up/down arrows only moved the
cursor within text — history browsing via FileHistory was attached
but inaccessible.

Two fixes:
1. Add up/down key bindings in normal input mode that call
   Buffer.auto_up()/auto_down(). These intelligently handle both:
   cursor movement when editing multi-line text, and history
   browsing when on the first/last line.

2. Pass append_to_history=True to buffer.reset() in the Enter
   handler so messages actually get saved to ~/.hermes_history.

History persists across sessions via FileHistory. The bindings are
filtered out during clarify, approval, and sudo prompts (which
have their own up/down handlers).

cli.py

@@ -2378,7 +2378,7 @@ class HermesCLI:
                     self._interrupt_queue.put(text)
                 else:
                     self._pending_input.put(text)
-                event.app.current_buffer.reset()
+                event.app.current_buffer.reset(append_to_history=True)
         
         @kb.add('escape', 'enter')
         def handle_alt_enter(event):
@@ -2423,6 +2423,24 @@ class HermesCLI:
                 self._approval_state["selected"] = min(max_idx, self._approval_state["selected"] + 1)
                 event.app.invalidate()
 
+        # --- History navigation: up/down browse history in normal input mode ---
+        # The TextArea is multiline, so by default up/down only move the cursor.
+        # Buffer.auto_up/auto_down handle both: cursor movement when multi-line,
+        # history browsing when on the first/last line (or single-line input).
+        _normal_input = Condition(
+            lambda: not self._clarify_state and not self._approval_state and not self._sudo_state
+        )
+
+        @kb.add('up', filter=_normal_input)
+        def history_up(event):
+            """Up arrow: browse history when on first line, else move cursor up."""
+            event.app.current_buffer.auto_up(count=event.arg)
+
+        @kb.add('down', filter=_normal_input)
+        def history_down(event):
+            """Down arrow: browse history when on last line, else move cursor down."""
+            event.app.current_buffer.auto_down(count=event.arg)
+
         @kb.add('c-c')
         def handle_ctrl_c(event):
             """Handle Ctrl+C - cancel interactive prompts, interrupt agent, or exit.