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/app/runtime/actions/oauth.rs

@@ -1,5 +1,7 @@
 //! OAuth PKCE flow — browser-based login for API providers.
 
+use tracing::{info, warn};
+
 /// Run a browser-based OAuth PKCE flow for the given provider.
 ///
 /// Flow: look up config by provider name ("zen"/"opencode", "openai",
@@ -15,6 +17,7 @@
 /// Return: a success message on completion, or an error if the flow fails
 /// at any step.
 pub(super) fn run_oauth_flow(provider: &str) -> anyhow::Result<String> {
+    info!(provider = provider, "starting OAuth flow");
     use zesdex_iam::domain::oauth::OAuthConfig;
     use zesdex_iam::domain::service::OAuthService;
     use zesdex_iam::application::oauth_service::OAuthServiceImpl;
@@ -86,20 +89,22 @@ pub(super) fn run_oauth_flow(provider: &str) -> anyhow::Result<String> {
 
     let (auth_url, state) = oauth_service.start_flow(&config, &redirect_uri)?;
     if auth_url.is_empty() {
-        tracing::warn!("[oauth] auth_url was empty for provider '{}'", provider);
+        warn!("OAuth auth_url was empty for provider '{}'", provider);
     } else if webbrowser::open(&auth_url).is_err() {
-        tracing::warn!(
-            "[oauth] could not open browser for '{}'; user must open URL manually:\n{}",
+        warn!(
+            "OAuth could not open browser for '{}'; user must open URL manually:\n{}",
             provider,
             auth_url
         );
     }
 
+    info!(provider = provider, "waiting for OAuth redirect");
     let code = server.wait_for_code(120_000, &state)?;
 
     oauth_service
         .complete_flow(&config, &redirect_uri, &code, &state)
         .map_err(|e| anyhow::anyhow!("{e}"))?;
 
+    info!(provider = provider, "OAuth flow completed");
     Ok(format!("Successfully authenticated with {provider}."))
 }