feat: add fake trading module with crypto, stocks, forex and gold

Paper trading system with 5 commands (trade_topup, trade_buy,
trade_sell, trade_convert, trade_stats). Supports VN stocks via TCBS,
crypto via CoinGecko, forex via ER-API, and gold via PAX Gold proxy.
Per-user portfolio stored in KV with 60s price caching. 54 new tests.

tests/modules/trading/symbols.test.js

@@ -0,0 +1,46 @@
+import { describe, expect, it } from "vitest";
+import {
+  CURRENCIES,
+  SYMBOLS,
+  getSymbol,
+  listSymbols,
+} from "../../../src/modules/trading/symbols.js";
+
+describe("trading/symbols", () => {
+  it("SYMBOLS has 9 entries across 3 categories", () => {
+    expect(Object.keys(SYMBOLS)).toHaveLength(9);
+    const cats = new Set(Object.values(SYMBOLS).map((s) => s.category));
+    expect(cats).toEqual(new Set(["crypto", "stock", "others"]));
+  });
+
+  it("getSymbol is case-insensitive", () => {
+    const btc = getSymbol("btc");
+    expect(btc).toBeDefined();
+    expect(btc.symbol).toBe("BTC");
+    expect(btc.category).toBe("crypto");
+
+    expect(getSymbol("Tcb").symbol).toBe("TCB");
+  });
+
+  it("getSymbol returns undefined for unknown symbols", () => {
+    expect(getSymbol("NOPE")).toBeUndefined();
+    expect(getSymbol("")).toBeUndefined();
+    expect(getSymbol(null)).toBeUndefined();
+  });
+
+  it("CURRENCIES contains VND and USD", () => {
+    expect(CURRENCIES.has("VND")).toBe(true);
+    expect(CURRENCIES.has("USD")).toBe(true);
+    expect(CURRENCIES.has("EUR")).toBe(false);
+  });
+
+  it("listSymbols returns grouped output", () => {
+    const out = listSymbols();
+    expect(out).toContain("Crypto:");
+    expect(out).toContain("BTC — Bitcoin");
+    expect(out).toContain("Stocks:");
+    expect(out).toContain("TCB — Techcombank");
+    expect(out).toContain("Others:");
+    expect(out).toContain("GOLD — Gold");
+  });
+});