feat(stalk): add github + youtube profile stalk endpoints

Ported from Shirokami-API scraper/stalk/{github,youtube}.js:
- /stalk/github (GitHub public API profile)
- /stalk/youtube (ytInitialData parse from /videos subpage:
  handles lockupViewModel (new), videoRenderer, gridVideoRenderer,
  shortsLockupViewModel; channel metadata + top-5 videos)

Also fix misc harga-emas main price to smallest-gram (1gr).

src/presentation/handler/stalk.rs

@@ -0,0 +1,44 @@
+//! Axum handlers for stalk (profile/user lookups).
+//!
+//! Ported from Shirokami-API `scraper/stalk/*.js`.
+
+use axum::extract::Query;
+use axum::http::StatusCode;
+use axum::Json;
+use serde::Deserialize;
+use serde_json::Value;
+
+use crate::application::stalk as use_cases;
+use crate::presentation::error::AppError;
+
+/// Query params for stalk endpoints.
+#[derive(Deserialize)]
+pub struct StalkParams {
+    pub username: Option<String>,
+    pub user_id: Option<String>,
+    pub userid: Option<String>,
+    pub zone_id: Option<String>,
+    pub zoneid: Option<String>,
+}
+
+/// GET /stalk/github?username=asepharyana
+pub async fn github_handler(
+    Query(params): Query<StalkParams>,
+) -> Result<(StatusCode, Json<Value>), AppError> {
+    let username = params
+        .username
+        .ok_or_else(|| AppError::BadRequest("Missing 'username' parameter".to_string()))?;
+    let result = use_cases::github(&username).await?;
+    Ok((StatusCode::OK, Json(result)))
+}
+
+/// GET /stalk/youtube?username=<handle>
+pub async fn youtube_handler(
+    Query(params): Query<StalkParams>,
+) -> Result<(StatusCode, Json<Value>), AppError> {
+    let username = params
+        .username
+        .ok_or_else(|| AppError::BadRequest("Missing 'username' parameter".to_string()))?;
+    let result = use_cases::youtube(&username).await?;
+    Ok((StatusCode::OK, Json(result)))
+}