docs: add model, small_model, default_agent fields to KILO_SPEC.md

Updated documentation to reflect official JSON Schema:
- model: global default model
- small_model: small model for titles/subtasks
- default_agent: default agent (must be primary mode)
- skills.urls: URLs to fetch skills from

.kilo/KILO_SPEC.md

@@ -151,8 +151,12 @@ Main configuration file with JSON Schema support.
   "$schema": "https://app.kilo.ai/config.json",
   "instructions": [".kilo/rules/*.md"],
   "skills": {
-    "paths": [".kilo/skills"]
+    "paths": [".kilo/skills"],
+    "urls": ["https://example.com/.well-known/skills/"]
   },
+  "model": "qwen/qwen3.6-plus:free",
+  "small_model": "openai/llama-3.1-8b-instant",
+  "default_agent": "orchestrator",
   "agent": {
     "agent-name": {
       "description": "Agent description",
@@ -178,6 +182,10 @@ Main configuration file with JSON Schema support.
 | `$schema` | string | JSON Schema URL for validation |
 | `instructions` | array | Glob patterns for rule files to load |
 | `skills.paths` | array | Directories containing skill modules |
+| `skills.urls` | array | URLs to fetch skills from |
+| `model` | string | Global default model (provider/model-id) |
+| `small_model` | string | Small model for titles/subtasks |
+| `default_agent` | string | Default agent when none specified (must be primary) |
 | `agent` | object | Agent definitions keyed by agent name |
 
 ### Agent Configuration Fields