feat(mcp): do mcp tool call from cli args

[burmudar]

• basic sse resposne parsing
• remove zero / nil arguments before making the request

Part of SRCH-2167

Test plan

Tested with go run ./cmd/src mcp commit-search -repos "sourcegraph/sourcegraph" -count 1 | tail -n 1 | jq

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "content": [
      {
        "type": "text",
        "text": "{\"query\":\"type:commit repo:sourcegraph/sourcegraph count:1\",\"totalCount\":1,\"commits\":[{\"repository\":\"github.com/sourcegraph/sourcegraph\",\"commit\":\"7cf5c82\",\"author\":\"Erik Seliger \\u003cerikseliger@me.com\\u003e\",\"date\":\"2025-11-28\",\"title\":\"Remove enable-simple-search (#8064)\",\"message\":\"Remove enable-simple-search (#8064)\\n\\nNot polished, never moved out of experimental, not implemented in\\nSvelte.\"}],\"limitHit\":true}"
      }
    ],
    "structuredContent": {
      "commits": [
        {
          "author": "Erik Seliger <erikseliger@me.com>",
          "commit": "7cf5c82",
          "date": "2025-11-28",
          "message": "Remove enable-simple-search (#8064)\n\nNot polished, never moved out of experimental, not implemented in\nSvelte.",
          "repository": "github.com/sourcegraph/sourcegraph",
          "title": "Remove enable-simple-search (#8064)"
        }
      ],
      "limitHit": true,
      "query": "type:commit repo:sourcegraph/sourcegraph count:1",
      "totalCount": 1
    }
  }
}

[burmudar]

This change is part of the following stack:

• feat(mcp): add script to dump mcp tool list #1211
  • feat(mcp): parse mcp tool json #1212
    • feat(mcp): add mcp list-tools to list available tool calls #1213
      • feat(mcp): build flagset from mcp input schema to parse args #1215
        • feat(mcp): do mcp tool call from cli args #1216 ◀

_{Change managed by git-spice.}