feat(antigravity): add Gemini 3.7 Flash models (#3286, #3281)

Add gemini-3.7-flash and its tiered high/medium/low variants to the
Antigravity and Gemini registries, with matching capabilities, pricing
and Antigravity quota tracking.

extractModel now recognises gemini-3.7-flash-tiered alongside 3.6 and
derives the version from the request, so thinkingLevel still maps to the
right tiered alias.

Closes #3286
Closes #3281

tests/unit/gemini-3.7-antigravity.test.js

@@ -0,0 +1,36 @@
+import { describe, it, expect } from "vitest";
+import { getCapabilitiesForModel } from "../../open-sse/providers/capabilities.js";
+import antigravityRegistry from "../../open-sse/providers/registry/antigravity.js";
+import geminiRegistry from "../../open-sse/providers/registry/gemini.js";
+import { MODEL_PRICING } from "../../open-sse/providers/pricing.js";
+
+describe("Gemini 3.7 Flash Support & Config (#3286, #3281)", () => {
+  it("registers gemini-3.7-flash tiered models in antigravity provider registry", () => {
+    const agIds = antigravityRegistry.models.map(m => m.id);
+    expect(agIds).toContain("gemini-3.7-flash-high");
+    expect(agIds).toContain("gemini-3.7-flash-medium");
+    expect(agIds).toContain("gemini-3.7-flash-low");
+    expect(agIds).not.toContain("gemini-3.7-flash");
+  });
+
+  it("registers gemini-3.7-flash in gemini provider registry", () => {
+    const geminiIds = geminiRegistry.models.map(m => m.id);
+    expect(geminiIds).toContain("gemini-3.7-flash");
+  });
+
+  it("resolves capabilities correctly for gemini-3.7 models with official limits", () => {
+    const caps = getCapabilitiesForModel("antigravity", "gemini-3.7-flash-high");
+    expect(caps.vision).toBe(true);
+    expect(caps.reasoning).toBe(true);
+    expect(caps.thinkingFormat).toBe("gemini-level");
+    expect(caps.contextWindow).toBe(1048576);
+    expect(caps.maxOutput).toBe(65536);
+  });
+
+  it("defines pricing matching gemini-3.6-flash baseline", () => {
+    expect(MODEL_PRICING["gemini-3.7-flash"]).toEqual(MODEL_PRICING["gemini-3.6-flash"]);
+    expect(MODEL_PRICING["gemini-3.7-flash-high"]).toEqual(MODEL_PRICING["gemini-3.6-flash-high"]);
+    expect(MODEL_PRICING["gemini-3.7-flash-medium"]).toEqual(MODEL_PRICING["gemini-3.6-flash-medium"]);
+    expect(MODEL_PRICING["gemini-3.7-flash-low"]).toEqual(MODEL_PRICING["gemini-3.6-flash-low"]);
+  });
+});