docs: Add Rustdoc to list mode's show_list_structured function

Co-authored-by: aider (openai/andrew/openrouter/sonoma-sky-alpha) <aider@aider.chat>

PLAN.md

@@ -144,24 +144,24 @@ Private helpers (e.g., internal `fn` without `pub`) are not flagged, as they don
     - `mode_get()` function: Partial.
     - `TeeReader` struct and impl `Read`: No docs.
 
-21. **src/args.rs**
+21. **src/args.rs** [DONE]
     - Structs (`Args`, `ModeArgs`, `ItemArgs`, `OptionsArgs`, `NumberOrString`): Partial.
     - Impl `FromStr` for `NumberOrString`: No doc.
     - `validate()` method on `Args`: No doc.
 
-22. **src/parser/filter_parser.rs**
+22. **src/parser/filter_parser.rs** [DONE]
     - `FilterParser` struct: No doc.
     - `parse_filter_string()` function: No doc.
     - Tests: No docs needed.
 
-23. **src/modes/server/api/mcp.rs**
+23. **src/modes/server/api/mcp.rs** [DONE]
     - `McpRequest` struct: No doc.
     - `handle_mcp_request()` function: No doc.
 
-24. **src/filter_plugin/utils.rs**
+24. **src/filter_plugin/utils.rs** [DONE]
     - `create_filter_chain()` and `parse_number()` functions: Partial.
 
-25. **src/modes/list.rs**
+25. **src/modes/list.rs** [DONE]
     - `mode_list()` function: Partial.
     - `ListItem` struct: No doc.
     - Helper functions (`apply_color`, `apply_attribute`, `show_list_structured`): No docs.