feat: Upgrade Codebase Agent to Claude Sonnet 4.5

Update model version across workflow and documentation:

- Workflow: claude-sonnet-4-5-20250929 (Anthropic API)
- Docs: claude-sonnet-4-5-20250929 (Anthropic API example)
- Docs: claude-sonnet-4-5@20250929 (Vertex AI example)
- Cost section: Updated to reflect Sonnet 4.5 model name

Sonnet 4.5 provides improved performance and capabilities
over the previous 3.5 Sonnet model.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: jeremyeder

.github/workflows/codebase-agent.yml

@@ -150,7 +150,7 @@ If this is a help request, provide:
 3. Relevant documentation or examples"""
 
           message = client.messages.create(
-              model="claude-3-5-sonnet-20241022",
+              model="claude-sonnet-4-5-20250929",
               max_tokens=2000,
               messages=[{"role": "user", "content": prompt}]
           )

docs/patterns/codebase-agent.md

@@ -258,7 +258,7 @@ jobs:
           # Call AI (Anthropic API or Vertex AI)
           client = Anthropic(api_key=os.environ['ANTHROPIC_API_KEY'])
           message = client.messages.create(
-              model="claude-3-5-sonnet-20241022",
+              model="claude-sonnet-4-5-20250929",
               max_tokens=2000,
               messages=[{
                   "role": "user",
@@ -299,7 +299,7 @@ client = AnthropicVertex(
 )
 
 message = client.messages.create(
-    model="claude-3-5-sonnet-v2@20241022",
+    model="claude-sonnet-4-5@20250929",
     max_tokens=2000,
     messages=[{"role": "user", "content": prompt}]
 )
@@ -350,7 +350,7 @@ concurrency:
 
 ### Cost Estimate
 
-**Vertex AI (Claude 3.5 Sonnet)**:
+**Vertex AI (Claude Sonnet 4.5)**:
 
 - Input: $3.00/1M tokens
 - Output: $15.00/1M tokens