feat(misc): add misc endpoints (currency-converter, harga-emas, kurs-bca, server-info)

Ported from Shirokami-API scraper/misc/*.js:
- /misc/currency-converter (wise.com scrape, amount/from/to)
- /misc/harga-emas (harga-emas.org Antam table)
- /misc/kurs-bca (bca.co.id jual/beli)
- /misc/server-info (OS/CPU/RAM/disk from /proc)

Also: remove /download/tiktok/v2 + /download/twitter/v2 as separate routes;
douyin.wtf + twitsave now internal fallback steps in the primary
fetch_tiktok/fetch_twitter chains (v2 = fallback per user directive).

src/presentation/handler/misc.rs

@@ -0,0 +1,50 @@
+//! Axum handlers for misc utility endpoints.
+//!
+//! Ported from Shirokami-API `scraper/misc/*.js`.
+
+use axum::extract::Query;
+use axum::http::StatusCode;
+use axum::Json;
+use serde::Deserialize;
+use serde_json::Value;
+
+use crate::application::misc as use_cases;
+use crate::presentation::error::AppError;
+
+/// Query params for currency converter.
+#[derive(Deserialize)]
+pub struct CurrencyParams {
+    pub amount: Option<f64>,
+    pub from: Option<String>,
+    pub to: Option<String>,
+}
+
+/// GET /misc/currency-converter?amount=100&from=USD&to=IDR
+pub async fn currency_converter_handler(
+    Query(params): Query<CurrencyParams>,
+) -> Result<(StatusCode, Json<Value>), AppError> {
+    let amount = params.amount.unwrap_or(1.0);
+    let from = params.from.unwrap_or_else(|| "USD".to_string());
+    let to = params.to.unwrap_or_else(|| "IDR".to_string());
+
+    let result = use_cases::currency_converter(amount, &from, &to).await?;
+    Ok((StatusCode::OK, Json(result)))
+}
+
+/// GET /misc/harga-emas
+pub async fn harga_emas_handler() -> Result<(StatusCode, Json<Value>), AppError> {
+    let result = use_cases::harga_emas().await?;
+    Ok((StatusCode::OK, Json(result)))
+}
+
+/// GET /misc/kurs-bca
+pub async fn kurs_bca_handler() -> Result<(StatusCode, Json<Value>), AppError> {
+    let result = use_cases::kurs_bca().await?;
+    Ok((StatusCode::OK, Json(result)))
+}
+
+/// GET /misc/server-info
+pub async fn server_info_handler() -> Result<(StatusCode, Json<Value>), AppError> {
+    let result = use_cases::server_info().await?;
+    Ok((StatusCode::OK, Json(result)))
+}