fix(minimax): Bổ sung MiniMax-M3 + cập nhật Quota Tracker coding/CN

Squash-merge PR #1631 (decolua/9router) — chỉ lấy file code + test, bỏ docs.

- feat(minimax): add MiniMax-M3 to intl + cn provider models (targetFormat claude)
- feat(minimax): add MiniMax-M3 pricing entry
- fix(minimax): translate Claude body khi content=null (M3 thinking-only)
- fix(minimax): hiển thị quota M-series bucket "general"/"MiniMax-M*" + percent-only
- test: minimax usage / model registration / pricing

Co-Authored-By: Claude <noreply@anthropic.com>
Co-authored-by: Cursor <cursoragent@cursor.com>

tests/unit/provider-pricing-minimax-m3.test.js

@@ -0,0 +1,29 @@
+import { describe, it, expect } from "vitest";
+import { MODEL_PRICING } from "../../src/shared/constants/pricing.js";
+
+describe("MiniMax-M3 pricing", () => {
+  it("includes MiniMax-M3 in MODEL_PRICING", () => {
+    expect(MODEL_PRICING["MiniMax-M3"]).toBeDefined();
+  });
+
+  it("MiniMax-M3 pricing has numeric shape (input, output, cached)", () => {
+    const pricing = MODEL_PRICING["MiniMax-M3"];
+    expect(pricing).toMatchObject({
+      input: expect.any(Number),
+      output: expect.any(Number),
+      cached: expect.any(Number),
+    });
+  });
+
+  it("MiniMax-M3 input price matches the design spec (0.30)", () => {
+    expect(MODEL_PRICING["MiniMax-M3"].input).toBe(0.30);
+  });
+
+  it("MiniMax-M3 output price matches the design spec (1.20)", () => {
+    expect(MODEL_PRICING["MiniMax-M3"].output).toBe(1.20);
+  });
+
+  it("MiniMax-M3 cached price matches the design spec (0.06)", () => {
+    expect(MODEL_PRICING["MiniMax-M3"].cached).toBe(0.06);
+  });
+});