feat(models): add grok-4.6 and make it the xAI flagship (#6624)

Verified every field against xAI's live API with the staging hosted key:
context_length 500000, $2.00/$0.50/$6.00 per 1M, temperature capped at 2,
tool calling and max_completion_tokens both accepted.

Also feature the latest blog post.

apps/sim/content/blog/secret-provenance/index.mdx

@@ -13,7 +13,7 @@ ogAlt: 'Sim secret provenance technical overview'
 about: ['Security', 'Execution']
 timeRequired: PT12M
 canonical: https://www.sim.ai/blog/secret-provenance
-featured: false
+featured: true
 draft: false
 faq:
   - q: "How does Sim keep API keys out of workflow execution logs?"

apps/sim/providers/models.test.ts

@@ -362,13 +362,14 @@ describe('kimi provider definition', () => {
 describe('xai provider definition', () => {
   const xai = PROVIDER_DEFINITIONS.xai
 
-  it('is registered with grok-4.5 as the default model', () => {
+  it('is registered with grok-4.6 as the default model', () => {
     expect(xai).toBeDefined()
     expect(xai.id).toBe('xai')
-    expect(xai.defaultModel).toBe('grok-4.5')
+    expect(xai.defaultModel).toBe('grok-4.6')
   })
 
   it('is included in getHostedModels since Sim provides the xAI key server-side', () => {
+    expect(getHostedModels()).toContain('grok-4.6')
     expect(getHostedModels()).toContain('grok-4.5')
   })
 })

apps/sim/providers/models.ts

@@ -2135,7 +2135,7 @@ export const PROVIDER_DEFINITIONS: Record<string, ProviderDefinition> = {
     fileAttachment: { maxBytes: 20 * 1024 * 1024, strategy: 'remote-url' },
     name: 'xAI',
     description: "xAI's Grok models",
-    defaultModel: 'grok-4.5',
+    defaultModel: 'grok-4.6',
     modelPatterns: [/^grok/],
     icon: xAIIcon,
     color: '#555555',
@@ -2143,6 +2143,21 @@ export const PROVIDER_DEFINITIONS: Record<string, ProviderDefinition> = {
       toolUsageControl: true,
     },
     models: [
+      {
+        id: 'grok-4.6',
+        pricing: {
+          input: 2.0,
+          cachedInput: 0.5,
+          output: 6.0,
+          updatedAt: '2026-08-12',
+        },
+        capabilities: {
+          temperature: { min: 0, max: 2 },
+        },
+        contextWindow: 500000,
+        releaseDate: '2026-08-12',
+        recommended: true,
+      },
       {
         id: 'grok-4.5',
         pricing: {
@@ -2155,7 +2170,6 @@ export const PROVIDER_DEFINITIONS: Record<string, ProviderDefinition> = {
         },
         contextWindow: 500000,
         releaseDate: '2026-07-08',
-        recommended: true,
       },
       {
         id: 'grok-4.3',