docs: tambah doc comment, logging, dan inline comments di semua 255 file

Meliputi:
- File-level //! doc comment: tujuan file, alur kerja, komponen utama
- Function-level /// doc comment: apa, parameter, return, flow, edge cases
- Struct/enum/trait /// doc comment: peran, field docs
- Tracing logging (tracing::info!/debug!/trace!/warn!/error!) di setiap fungsi
- Inline comments untuk variable dan branching logic penting
- Seluruh 8 crates di workspace: zesdex-backend, zesdex-cms, zesdex-entities,
  zesdex-iam, zesdex-infra, zesdex-ipc, zesdex-middleware, zesdex-utils
- Build: 0 errors, 242/242 tests passed

crates/zesdex-backend/src/model/agent_def/builtin.rs

@@ -1,5 +1,16 @@
 #![allow(dead_code)]
 //! Hardcoded built-in subagent definitions (coder, reviewer, researcher, planner).
+//!
+//! These agents are always available regardless of user or session config.
+//! They provide the default set of roles shipped with the application.
+//!
+//! ## Available agents
+//! | Agent | Purpose | Key tools |
+//! |-------|---------|-----------|
+//! | coder | Write/edit code | read, write, edit, bash, lsp_* |
+//! | reviewer | Review code for correctness/safety | read, grep, lsp_diagnostics |
+//! | researcher | Search and summarise | read, grep, bash, search_web |
+//! | planner | Break down tasks into steps | read, write, edit, bash, todo_* |
 use crate::app::subagent::spawn::AgentDefinition;
 
 /// Build the fixed list of built-in agent definitions shipped with zesdex.
@@ -34,6 +45,7 @@ pub fn builtin_agents() -> Vec<AgentDefinition> {
                 "lsp_completion".to_string(),
                 "lsp_disconnect".to_string(),
             ])
+            // Unlimited steps — the coder runs until the task is done.
             .with_max_steps(usize::MAX),
         AgentDefinition::new("reviewer".to_string(), "reviewer".to_string())
             .with_system_prompt(