docs(release): add API reference update + fix JSON syntax in 20260108.1 release notes

**Problem:**
- Malformed JSON in whats-new.json (missing closing bracket in bugfixes section)
- API reference update not mentioned in release notes
- GitHub billing fix from today not documented

**Solution:**
- Fixed JSON syntax error in bugfixes array
- Added GitHub Copilot billing cache fix to bugfixes
- Added API reference documentation update to improvements
- User-facing description: Help → API Reference now comprehensive

**Testing:**
✅ JSON validation: PASS (python3 -m json.tool)

Author: fewtarius

Resources/whats-new.json

@@ -50,6 +50,12 @@
           "description": "Renamed 'API Endpoints' to 'Remote Providers' throughout UI for consistency. Tab label and section headers now match."
         },
         {
+          "id": "github-billing-cache-fix",
+          "icon": "creditcard.fill",
+          "title": "GitHub Copilot Billing Display Fixed",
+          "description": "Fixed caching issues that prevented billing data from updating properly. GitHub Copilot usage and billing information now displays correctly."
+        }
+      ],
       "improvements": [
         {
           "id": "ram-based-recommendations",
@@ -86,12 +92,18 @@
           "icon": "arrow.triangle.branch",
           "title": "Seamless Wizard Integration",
           "description": "The onboarding wizard appears automatically when needed and integrates smoothly with SAM's main interface. Once you've configured a provider or downloaded a model, the wizard disappears and you see the normal welcome screen."
-        }
-      ] {
+        },
+        {
           "id": "onboarding-progress-indicators",
           "icon": "chart.line.uptrend.xyaxis",
           "title": "Download Progress in Onboarding",
           "description": "Onboarding wizard now shows percentage-based progress bars when downloading models. Visual feedback makes the setup process more transparent."
+        },
+        {
+          "id": "api-reference-update",
+          "icon": "book.fill",
+          "title": "Complete API Reference Documentation",
+          "description": "Help → API Reference now includes comprehensive documentation for all 20 endpoints, including new autonomous workflow, tool interaction, and model management APIs. All parameters verified against implementation with examples and detailed descriptions."
         }
       ]
     },