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/subagent/event.rs

@@ -1,5 +1,10 @@
+//! Event variants that a running subagent can emit to its parent via the
+//! shared mpsc channel.
+
 use serde_json::Value;
 
+/// Progress and outcome events emitted by `run_subagent` as it processes
+/// LLM responses and tool calls.
 #[derive(Debug, Clone)]
 pub enum SubagentEvent {
     StepCompleted {