feat: 拆分 providers.json 为按 Provider 独立文件

将 compute/providers.json（54KB, 14 providers, 99 models）拆分为
compute/providers/ 目录下的独立 JSON 文件，便于维护和按需更新。

新增文件：
- compute/providers/_index.json — 加载顺序索引（保证 digest 确定性）
- compute/providers/{provider}.json × 14 — 各 provider 独立配置

保留 compute/providers.json 供旧客户端向后兼容（过渡期）。

presetDataVersion: 2 → 3

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

compute/providers/ollama.json

@@ -0,0 +1,29 @@
+{
+  "id": "provider-local-ollama",
+  "provider": "ollama",
+  "label": "本地 Ollama",
+  "baseUrl": "http://localhost:11434/v1",
+  "apiFormat": "openai-completions",
+  "apiKeyRef": "",
+  "apiKeyVerified": false,
+  "enabled": false,
+  "status": "unconfigured",
+  "services": [
+    "chat"
+  ],
+  "models": [
+    {
+      "modelName": "llama3.1:70b",
+      "displayName": "Llama 3.1 70B",
+      "serviceType": "chat",
+      "description": "本地运行的 Llama 3.1 70B",
+      "contextWindow": 131072,
+      "capabilities": [
+        "chat",
+        "code",
+        "reasoning"
+      ],
+      "extra": {}
+    }
+  ]
+}