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/model/app_config.rs

@@ -1,6 +1,11 @@
+//! Application-level configuration: LLM providers, model roles, and defaults,
+//! persisted to `app_config.json` in the store directory.
+
 use serde::{Deserialize, Serialize};
 use std::collections::HashMap;
 
+/// Top-level application config: registered providers, named model roles,
+/// and which provider/model to use by default.
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct AppConfig {
     pub providers: HashMap<String, ProviderConfig>,
@@ -9,6 +14,7 @@ pub struct AppConfig {
     pub default_model: String,
 }
 
+/// Connection details for a single LLM provider (base URL, API key source).
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct ProviderConfig {
     pub api_base: String,
@@ -17,6 +23,8 @@ pub struct ProviderConfig {
     pub default_api_key: Option<String>,
 }
 
+/// A named role (e.g. "default") mapping to a specific provider/model and
+/// its generation parameters.
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct ModelRole {
     pub provider: String,
@@ -57,6 +65,17 @@ impl Default for AppConfig {
 }
 
 impl AppConfig {
+    /// Load app config from disk, falling back to defaults on any failure.
+    ///
+    /// Flow: read `<store>/app_config.json` → JSON-parse → on missing file
+    /// or parse error, use `Self::default()` → merge any default providers
+    /// not already present in the loaded config.
+    ///
+    /// Why: the merge step lets newly-added default providers (e.g. a new
+    /// release adding a provider) appear even in configs saved by older
+    /// versions, without clobbering user-edited entries with the same name.
+    ///
+    /// Return: a fully-populated `AppConfig`, never fails.
     pub fn load() -> Self {
         let store = super::store::Store::new();
         let path = store.base_dir.join("app_config.json");