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/view/theme.rs

@@ -1,5 +1,20 @@
+//! Central color theme for the TUI.
+//!
+//! Flow: defines a single `Theme` marker struct with associated `Color`
+//! consts, consumed by every `view/*` render function so styling stays
+//! consistent and changeable from one place.
+//!
+//! Why: a zero-sized struct with associated consts (rather than an enum
+//! or a runtime-configured palette) keeps color lookups compile-time
+//! constant and allocation-free.
+
 use ratatui::style::Color;
 
+/// Central palette of terminal colors used across all TUI render functions.
+///
+/// Why: a zero-sized marker struct holding only associated consts, so
+/// every view module references colors as `Theme::NAME` instead of
+/// hardcoding `ratatui::style::Color` values inline.
 pub struct Theme;
 
 impl Theme {