add multi-currency master CRUD (Phase 2)

- add currencyadapter.js: list (with pagination+keyword), detail, history, create, update (auto-log rate change to tbl_currency_log), delete (soft), convertAmount helper
- add controllers/currency.js and routes/currency.js, auto-mounted at /currency
- update dbproc.js: configurable port via HOSTPORT env variable

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

config/dbproc.js

@@ -7,7 +7,8 @@ const dbcon = mysql.createConnection({
     database : process.env.DBHOST,
     acquireTimeout: 30000,
     insecureAuth: true,
-    timezone: 'utc'
+    timezone: 'utc',
+    port    : process.env.HOSTPORT ?? 3306 
 });
 
 dbcon.connect(function(err) {