fix(tui): prevent trailing space in picker-command completions

Commands that open pickers (/model, /skin, /personality) previously
received a trailing space in their completions to keep the dropdown
visible in the classic CLI. However, the TUI's submit handler applies
the completion when Enter is pressed and the result differs from the
input — so '/model' + space became '/model ' and the command was never
executed.

Picker commands now omit the trailing space for exact matches, allowing
Enter to submit and open the picker. Non-picker commands (/help, etc.)
are unaffected.

hermes_cli/commands.py

@@ -862,6 +862,12 @@ class SlashCommandCompleter(Completer):
         except Exception:
             return {}
 
+    # Commands that open pickers when run without arguments.
+    # These should NOT receive a trailing space in completions because:
+    # - The TUI's submit handler applies completions on Enter if input differs
+    # - Adding space makes "/model" → "/model " which blocks picker execution
+    _PICKER_COMMANDS = frozenset({"model", "skin", "personality"})
+
     @staticmethod
     def _completion_text(cmd_name: str, word: str) -> str:
         """Return replacement text for a completion.
@@ -870,8 +876,17 @@ class SlashCommandCompleter(Completer):
         returning ``help`` would be a no-op and prompt_toolkit suppresses the
         menu. Appending a trailing space keeps the dropdown visible and makes
         backspacing retrigger it naturally.
+
+        However, commands that open pickers (model, skin, personality) should
+        NOT get a trailing space — the TUI would apply the completion on Enter
+        and block the picker from opening.
         """
-        return f"{cmd_name} " if cmd_name == word else cmd_name
+        if cmd_name != word:
+            return cmd_name
+        # Don't add space for picker commands — allows Enter to execute them
+        if cmd_name in SlashCommandCompleter._PICKER_COMMANDS:
+            return cmd_name
+        return f"{cmd_name} "
 
     @staticmethod
     def _extract_path_word(text: str) -> str | None: