Migrate Policy tools to new tool design

[alzimmermsft]

What does this PR do?

Migrates Policy tools to new design where Register and Bind options are based on Option attributes.

GitHub issue number?

[Link to the GitHub issue this PR addresses]

Pre-merge Checklist

• Required for All PRs
  • Read contribution guidelines
  • PR title clearly describes the change
  • Commit history is clean with descriptive messages (cleanup guide)
  • Added comprehensive tests for new/modified functionality
  • Created a changelog entry if the change falls among the following: new feature, bug fix, UI/UX update, breaking change, or updated dependencies. Follow the changelog entry guide
• For MCP tool changes:
  • One tool per PR: This PR adds or modifies only one MCP tool for faster review cycles
  • Updated servers/Azure.Mcp.Server/README.md and/or servers/Fabric.Mcp.Server/README.md documentation
  • Validate README.md changes running the script ./eng/scripts/Process-PackageReadMe.ps1. See Package README
  • For new or modified tool descriptions, ran ToolDescriptionEvaluator and obtained a score of 0.4 or more and a top 3 ranking for all related test prompts
  • For tools with new names, including new tools or renamed tools, update consolidated-tools.json
  • For renamed tools, follow the Tool Rename Checklist and tag the PR with the breaking-change label
  • For new tools associated with Azure services or publicly available tools/APIs/products, add URL to documentation in the PR description
• Extra steps for Azure MCP Server tool changes:
  • Updated command list in servers/Azure.Mcp.Server/docs/azmcp-commands.md
  • Ran ./eng/scripts/Update-AzCommandsMetadata.ps1 to update tool metadata in azmcp-commands.md (required for CI)
  • Updated test prompts in servers/Azure.Mcp.Server/docs/e2eTestPrompts.md
  • 👉 For Community (non-Microsoft team member) PRs:
    • Security review: Reviewed code for security vulnerabilities, malicious code, or suspicious activities before running tests (crypto mining, spam, data exfiltration, etc.)
    • Manual tests run: added comment /azp run mcp - pullrequest - live to run Live Test Pipeline

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[Copilot]

Pull request overview

This PR migrates Azure Policy tool(s) to the newer command/options design that relies on [Option] attributes (OptionBinder) instead of per-command RegisterOptions/BindOptions logic, and removes the Policy toolset’s direct dependency on System.CommandLine artifacts.

Changes:

• Updated PolicyAssignmentListCommand to the new SubscriptionCommand<TOptions, TResult> pattern and moved option declarations into PolicyAssignmentListOptions via [Option] attributes.
• Removed legacy Policy option definition scaffolding (PolicyOptionDefinitions) and the toolset’s System.CommandLine package reference/global usings.
• Adjusted unit tests to use SubscriptionCommandUnitTestsBase.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tools/Azure.Mcp.Tools.Policy/tests/Azure.Mcp.Tools.Policy.Tests/Assignment/PolicyAssignmentListCommandTests.cs	Switches to subscription-aware test base to support the new command constructor/options binding flow.
tools/Azure.Mcp.Tools.Policy/src/Services/PolicyService.cs	Adds explicit System.Text.Json import after removing Policy toolset global usings.
tools/Azure.Mcp.Tools.Policy/src/Options/PolicyOptionDefinitions.cs	Removes legacy System.CommandLine-based option definitions.
tools/Azure.Mcp.Tools.Policy/src/Options/Assignment/PolicyAssignmentListOptions.cs	Converts options to [Option] attributes and implements ISubscriptionOption.
tools/Azure.Mcp.Tools.Policy/src/GlobalUsings.cs	Removes Policy toolset global usings (previously included System.CommandLine and JSON usings).
tools/Azure.Mcp.Tools.Policy/src/Commands/Assignment/PolicyAssignmentListCommand.cs	Migrates to SubscriptionCommand<TOptions, TResult> and removes manual option registration/binding.
tools/Azure.Mcp.Tools.Policy/src/Azure.Mcp.Tools.Policy.csproj	Removes System.CommandLine dependency and updates Core project reference path.
servers/Azure.Mcp.Server/changelog-entries/1784220389040.yaml	Adds a changelog entry indicating a breaking change for Policy tools.