Add command: azmcp costmanagement query run

## Summary

Add a new `costmanagement` toolset starting with `azmcp costmanagement query run` that retrieves actual Azure costs from the Cost Management Query/Usage API for a subscription or resource group.

## Motivation

Azure MCP Server has no tool to retrieve actual Azure costs today. The only cost-adjacent tool is `azmcp pricing get`, which queries the public retail catalog (estimates, not actual spend). This gap was previously surfaced in:

- #1420 — `[ONBOARD] finops recommenders` (closed Done 2026-02 with no follow-up PR)
- #447 — `Create CostManagement Tool File Structure` (closed without merge 2025-10 due to inactivity)

AWS Billing MCP and GCP have analogous tools; Azure does not.

## Scope of this issue (PR1)

`azmcp costmanagement query run` — read-only, scoped to subscription (optionally narrowed to a resource group). Backed by the GA SDK `Azure.ResourceManager.CostManagement` 1.0.3.

```bash
azmcp costmanagement query run --subscription <sub>\
[--resource-group ] \
[--timeframe ] \
[--from ] [--to ] \
[--granularity ] \
[--group-by ]
```</sub>

Caller must have `Cost Management Reader` or `Reader` role on the scope.

PR is ready and will be opened from `francesco1501/mcp:feature/add-costmanagement-query` shortly.

cc @anannya03 (CODEOWNER of `tools/Azure.Mcp.Tools.Pricing/` and original assignee of #1420) — would appreciate a sanity check on the design before review.

Start by reviewing the analogous tools/Azure.Mcp.Tools.Pricing/ implementation and the Azure.ResourceManager.CostManagement 1.0.3 Query/Usage API. Check the proposed command options and subscription/resource-group scope against the API contract. Done means the read-only query command supports the listed timeframes, date range, granularity, and grouping options.

Written by the indexing model from the issue text.