REST API OpenAPI spec (#612)

* OpenAPI spec in specs/api.  Checked lint with redoc.

specs/api/components/schemas/mcp-tool/McpToolRequest.yaml

@@ -0,0 +1,17 @@
+type: object
+description: |
+  MCP tool request - execute Model Context Protocol tool.
+required:
+  - name
+properties:
+  name:
+    type: string
+    description: Tool name to execute
+    example: search
+  parameters:
+    type: object
+    description: Tool parameters (JSON object, auto-converted to string internally)
+    additionalProperties: {}
+    example:
+      query: quantum computing
+      limit: 10

specs/api/components/schemas/mcp-tool/McpToolResponse.yaml

@@ -0,0 +1,15 @@
+type: object
+description: MCP tool response
+properties:
+  text:
+    type: string
+    description: Text response from tool
+    example: Found 10 results for quantum computing...
+  object:
+    type: object
+    description: Structured response from tool (JSON object)
+    additionalProperties: {}
+    example:
+      results:
+        - title: Introduction to Quantum Computing
+          url: https://example.com/qc-intro