fix(tui): @folder: only yields directories, @file: only yields files

Reported during TUI v2 blitz testing: typing `@folder:` in the composer
pulled up .dockerignore, .env, .gitignore, and every other file in the
cwd alongside the actual directories. The completion loop yielded every
entry regardless of the explicit prefix and auto-rewrote each completion
to @file: vs @folder: based on is_dir — defeating the user's choice.

Also fixed a pre-existing adjacent bug: a bare `@file:` or `@folder:`
(no path) used expanded=="." as both search_dir AND match_prefix,
filtering the list to dotfiles only. When expanded is empty or ".",
search in cwd with no prefix filter.

- want_dir = prefix == "@folder:" drives an explicit is_dir filter
- preserve the typed prefix in completion text instead of rewriting
- three regression tests cover: folder-only, file-only, and the bare-
  prefix case where completions keep the `@folder:` prefix

hermes_cli/commands.py

@@ -924,12 +924,22 @@ class SlashCommandCompleter(Completer):
                     display_meta=meta,
                 )
 
-        # If the user typed @file: or @folder:, delegate to path completions
+        # If the user typed @file: / @folder: (or just @file / @folder with
+        # no colon yet), delegate to path completions.  Accepting the bare
+        # form lets the picker surface directories as soon as the user has
+        # typed `@folder`, without requiring them to first accept the static
+        # `@folder:` hint and re-trigger completion.
         for prefix in ("@file:", "@folder:"):
-            if word.startswith(prefix):
-                path_part = word[len(prefix):] or "."
+            bare = prefix[:-1]
+
+            if word == bare or word.startswith(prefix):
+                want_dir = prefix == "@folder:"
+                path_part = '' if word == bare else word[len(prefix):]
                 expanded = os.path.expanduser(path_part)
-                if expanded.endswith("/"):
+
+                if not expanded or expanded == ".":
+                    search_dir, match_prefix = ".", ""
+                elif expanded.endswith("/"):
                     search_dir, match_prefix = expanded, ""
                 else:
                     search_dir = os.path.dirname(expanded) or "."
@@ -945,15 +955,21 @@ class SlashCommandCompleter(Completer):
                 for entry in sorted(entries):
                     if match_prefix and not entry.lower().startswith(prefix_lower):
                         continue
-                    if count >= limit:
-                        break
                     full_path = os.path.join(search_dir, entry)
                     is_dir = os.path.isdir(full_path)
+                    # `@folder:` must only surface directories; `@file:` only
+                    # regular files.  Without this filter `@folder:` listed
+                    # every .env / .gitignore in the cwd, defeating the
+                    # explicit prefix and confusing users expecting a
+                    # directory picker.
+                    if want_dir != is_dir:
+                        continue
+                    if count >= limit:
+                        break
                     display_path = os.path.relpath(full_path)
                     suffix = "/" if is_dir else ""
-                    kind = "folder" if is_dir else "file"
                     meta = "dir" if is_dir else _file_size_label(full_path)
-                    completion = f"@{kind}:{display_path}{suffix}"
+                    completion = f"{prefix}{display_path}{suffix}"
                     yield Completion(
                         completion,
                         start_position=-len(word),