Enhance tool documentation and add new features

- Added module-level documentation for memory tools (`remember`, `recall`, `forget`) to clarify their purpose.
- Improved documentation in `recall.rs` and `remember.rs` to describe the functionality and flow of memory entry operations.
- Updated `mod.rs` to include descriptions for the tool trait and execution context.
- Enhanced `plan.rs` with detailed comments on plan-mode signaling tools.
- Documented text search tools in `search.rs` to explain their functionality.
- Improved sequential-thinking tool documentation in `seqthink.rs`.
- Added safety filter documentation in `shell_filter` for credential and git operations.
- Enhanced utility tools documentation, including `cd`, `dir_cache_update`, and `todowrite`.
- Improved rendering documentation in view modules (`chat`, `markdown`, `status`, `workflow`) to clarify rendering flows and purposes.

src/app/mode/help.rs

@@ -1,3 +1,5 @@
+//! Help mode: static help text and the action that opens/closes the help overlay.
+
 use crate::app::runtime::actions::Action;
 use crate::app::state::types::Overlay;
 
@@ -27,6 +29,12 @@ Slash commands:
   /lesson import    Import lessons
   /clear            Clear transcript";
 
+/// Route an incoming action while the help overlay is open.
+///
+/// Flow: `CloseOverlay` passes through unchanged; any other action is
+/// treated as "open help" (idempotent — re-opens the overlay it's already on).
+///
+/// Return: the `Action` to actually dispatch.
 pub fn handle_help_action(action: &Action) -> Action {
     match action {
         Action::CloseOverlay => Action::CloseOverlay,