Add MCP tool usage statistics to audit command

[Copilot]

The audit command now extracts MCP tool call statistics from gateway.jsonl files, providing both aggregated metrics and individual call records.

Changes

• Data structures (audit_report.go): Added MCPToolUsageData with server/tool summaries and individual call records
• Gateway parsing (gateway_logs.go): extractMCPToolUsageData() parses gateway.jsonl for tool call metadata (sizes, durations, timestamps)
• Console output (audit_report_render.go): Two tables showing server-level (requests, total I/O, avg duration) and tool-level (call count, total/max input/output sizes) statistics
• JSON export: New mcp_tool_usage field includes complete call history with per-call metadata

Output

Console:

MCP Tool Usage
==============

Server Statistics:
Server  | Requests | Tool Calls | Total Input | Total Output | Avg Duration
github  |       15 |         15 |      10.2KB |       45.8KB |       150ms

Tool Statistics:
Server | Tool             | Calls | Total In | Total Out | Max In | Max Out
github | search_issues    |     5 |   5.1KB  |   30.2KB  | 1.5KB  |  8.9KB

JSON:

{
  "mcp_tool_usage": {
    "summary": [{
      "server_name": "github",
      "tool_name": "search_issues",
      "call_count": 5,
      "total_input_size": 5230,
      "total_output_size": 30924,
      "max_input_size": 1536,
      "max_output_size": 9112
    }],
    "tool_calls": [{
      "timestamp": "2024-01-12T10:00:00Z",
      "server_name": "github",
      "tool_name": "search_issues",
      "input_size": 1024,
      "output_size": 5120,
      "duration": "145ms",
      "status": "success"
    }]
  }
}

Gateway logs contain call metadata (sizes, timestamps, durations) but not request/response payloads. Statistics are extracted when gateway.jsonl exists; gracefully skipped otherwise.

Original prompt

Make sure that the "audit" command generate table MCP tool calls usage and response size statistics (total, max size)

The JSON should also have every tool call request and response message attached for each tool

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