mcp(fix[docs]): Clarify parameter descriptions from tmux source

why: Several MCP tool parameter descriptions were ambiguous when
cross-referenced against the tmux C source code. LLMs using these tools
need precise format guidance to construct correct arguments.

Verified against:
- layout-set.c:43-49 for built-in layout names
- cmd-split-window.c for size format
- option_tools target format per scope
what:
- select_layout: list all 7 built-in layout names from tmux source
- option_tools target: document expected format per scope (session name,
  window ID '@1', pane ID '%1')

Author: tony

src/libtmux/mcp/tools/option_tools.py

@@ -76,7 +76,9 @@ def show_option(
     scope : str, optional
         Option scope: "server", "session", "window", or "pane".
     target : str, optional
-        Target session, window, or pane identifier.
+        Target identifier. For session scope: session name
+        (e.g. 'mysession'). For window scope: window ID (e.g. '@1').
+        For pane scope: pane ID (e.g. '%1'). Requires scope.
     global_ : bool
         Whether to query the global option.
     socket_name : str, optional
@@ -112,7 +114,9 @@ def set_option(
     scope : str, optional
         Option scope: "server", "session", "window", or "pane".
     target : str, optional
-        Target session, window, or pane identifier.
+        Target identifier. For session scope: session name
+        (e.g. 'mysession'). For window scope: window ID (e.g. '@1').
+        For pane scope: pane ID (e.g. '%1'). Requires scope.
     global_ : bool
         Whether to set the global option.
     socket_name : str, optional