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/tool/utility/pong.rs

@@ -1,8 +1,17 @@
+//! Trivial connectivity-check tool.
+//!
+//! Flow: read the optional `message` argument → echo it back prefixed
+//! with `"pong: "`, defaulting to `"pong"` when no message is supplied.
+//!
+//! Why: gives callers a cheap, dependency-free way to verify the tool
+//! harness is reachable and responding before running real work.
+
 use serde_json::{json, Value};
 use anyhow::Result;
 use super::super::Tool;
 use super::super::ToolCtx;
 
+/// Tool that echoes back a message; used for connectivity/latency checks.
 pub struct Pong;
 
 impl Tool for Pong {