feat(models): add GLM-5.3-Flash, DeepSeek V4 Vision, Grok 4.5/4.6

Vendors shipped four multimodal models the registry did not carry:

- glm-5.3-flash — z.ai's first natively multimodal GLM-5, 1M context,
  image + video + pdf input (glm, glm-cn, opencode-go)
- deepseek-v4-flash-vision-exp — image input at V4-Flash text parity,
  1M context / 384k output (deepseek, opencode-go)
- grok-4.6, grok-4.5 — 500k context; 4.6 has no text output limit (xai)

Capabilities needed hand entries because the existing globs mis-matched:
*glm-5* and *deepseek-v4* carry no vision, and *grok-4* would have capped
grok-4.6 at 256k instead of 500k. The grok-4.6 pattern sits above the
generic *grok-4* so it wins the first-match lookup.

Also corrects glm-4.6v / glm-4.5v, which were missing video input and
declared no maxOutput, and backfills glm-4.6v on glm-cn — zhipuai serves
it and the sibling provider already listed it.

tests/unit/opencode-go-models.test.js pins the opencode-go model list, so
its expected array moves with the registry.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

open-sse/providers/registry/xai.js

@@ -27,6 +27,8 @@ export default {
     refreshUrl: "https://auth.x.ai/oauth2/token",
   },
   models: [
+    { id: "grok-4.6", name: "Grok 4.6" },
+    { id: "grok-4.5", name: "Grok 4.5" },
     { id: "grok-4", name: "Grok 4" },
     { id: "grok-4-fast-reasoning", name: "Grok 4 Fast Reasoning" },
     { id: "grok-code-fast-1", name: "Grok Code Fast" },