Remove redundant manual EnsureApproval calls from MCP tools

[Copilot]

This PR removes all manual ToolApprovalManager.Instance.EnsureApproved() calls from MCP tool methods, ensuring that tool approval is controlled exclusively by the [RequiresApproval] attribute through the ToolApprovalWrapper system.

Problem

Many MCP tools had both:

1. [RequiresApproval] attributes on methods
2. Manual EnsureApproved() calls within the method implementations

This created redundant approval logic and violated the design principle that the [RequiresApproval] attribute should be the single source of truth for approval requirements.

Solution

Removed manual approval calls from methods WITH [RequiresApproval]:

• ShellTools.RunCommand()
• FileTools.WriteFile(), DeleteFile(), CreateDirectory()
• HttpTools.HttpRequest()
• CodeReviewTools.GenerateReviewComment()
• GitHubTools.PostPullRequestComment()

Removed manual approval calls from methods WITHOUT [RequiresApproval]:

• All read-only GitHub operations (GetPullRequest, GetPullRequestFiles, etc.)
• Code review analysis operations (AnalyzePullRequestForReview, ExtractCodePatterns)
• All Azure DevOps operations (6 methods)
• All OpenAI Vector Store operations (5 methods)

Impact

• ~200+ lines of redundant code removed
• Approval logic now centralized in ToolApprovalWrapper
• Cleaner, more maintainable codebase
• All 61 existing tests continue to pass

The approval system continues to work correctly - tools with [RequiresApproval] are automatically wrapped with approval logic, while tools without the attribute execute immediately.

Fixes #77.

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