fix: update default model from claude-sonnet-4-5 to claude-sonnet-4-6 (#1390)

CLAUDE_MEM_MODEL defaulted to the deprecated claude-sonnet-4-5 across source,
installer, tests, and documentation. Updated all references to claude-sonnet-4-6.

Closes #1390

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

docs/public/architecture/hooks.mdx

@@ -860,7 +860,7 @@ async startSession(session: ActiveSession, worker?: any) {
   const queryResult = query({
     prompt: messageGenerator,
     options: {
-      model: 'claude-sonnet-4-5',
+      model: 'claude-sonnet-4-6',
       disallowedTools: ['Bash', 'Read', 'Write', ...],  // Observer-only
       abortController: session.abortController
     }

docs/public/platform-integration.mdx

@@ -46,7 +46,7 @@ GET /api/context/recent?project=my-project&limit=3
 ### Environment Variables
 
 ```bash
-CLAUDE_MEM_MODEL=claude-sonnet-4-5          # Model for observations/summaries
+CLAUDE_MEM_MODEL=claude-sonnet-4-6          # Model for observations/summaries
 CLAUDE_MEM_CONTEXT_OBSERVATIONS=50          # Observations injected at SessionStart
 CLAUDE_MEM_WORKER_PORT=37777                # Worker service port
 CLAUDE_MEM_PYTHON_VERSION=3.13              # Python version for chroma-mcp