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/cd.rs

@@ -1,8 +1,11 @@
+//! `cd` tool: verify and resolve a workspace-relative directory path.
+
 use serde_json::{json, Value};
 use anyhow::{Result, anyhow};
 use super::super::Tool;
 use super::super::ToolCtx;
 
+/// Tool that resolves a workspace-relative path and reports whether it exists and is a dir.
 pub struct Cd;
 
 impl Tool for Cd {
@@ -27,6 +30,16 @@ impl Tool for Cd {
         })
     }
 
+    /// Resolve `path` against the workspace roots and report its status.
+    ///
+    /// Flow: extract `path` → `resolve_path` (sandboxed to `ctx.workspaces`) →
+    ///       check `exists()` and `is_dir()` → canonicalize → return canonical path.
+    ///
+    /// Why: the agent has no persistent cwd between tool calls; "cd" here is purely a
+    /// verification + canonicalization helper rather than a state change.
+    ///
+    /// Return: canonical path on success; explicit "does not exist" / "not a directory"
+    /// message (still `Ok`) so the model can react without treating it as an error.
     fn run(&self, ctx: &ToolCtx, args: &Value) -> Result<String> {
         let rel = args.get("path")
             .and_then(|v| v.as_str())