feat: OpsxDB 桌面数据库客户端首版入库

含工作台/连库多引擎字段与 SSH·SSL、结果编辑、Redis 键浏览、
Tauri 桌面与 docs/落地页；排除本地构建产物与 sidecar 二进制。

api/openapi.yaml

@@ -0,0 +1,61 @@
+openapi: 3.0.3
+info:
+  title: OpsxDB Server
+  version: 0.2.0
+  description: Database workbench API — sessions, metadata, SQL exec
+servers:
+  - url: http://127.0.0.1:8788
+paths:
+  /health:
+    get:
+      summary: Health check
+      responses:
+        "200":
+          description: OK
+  /api/health:
+    get:
+      summary: Health check
+      responses:
+        "200":
+          description: OK
+  /api/db/test-connection:
+    post:
+      summary: Ping a database without creating a session
+  /api/db/open:
+    post:
+      summary: Ping and create a server-side session (password stays on server)
+  /api/db/close:
+    post:
+      summary: Close a session
+  /api/db/databases:
+    post:
+      summary: List databases (sessionId or full conn)
+  /api/db/tables:
+    post:
+      summary: List tables in a database
+  /api/db/columns:
+    post:
+      summary: List columns of a table
+  /api/db/exec:
+    post:
+      summary: Execute SQL or Redis command
+  /api/ai/chat:
+    post:
+      summary: AI actions (currently stub)
+components:
+  schemas:
+    ConnReq:
+      type: object
+      properties:
+        driver: { type: string }
+        host: { type: string }
+        port: { type: integer }
+        user: { type: string }
+        password: { type: string }
+        database: { type: string }
+        service: { type: string }
+        ssl: { type: boolean }
+        sessionId: { type: string }
+        sql: { type: string }
+        table: { type: string }
+        limit: { type: integer }