Add performance benchmarking and set performance budgets

Description

Establish performance benchmarks and budgets to ensure the MCP server remains fast and responsive.

v1.0 split

For v1.0 release readiness, we split out a smaller, lower-risk slice (non-blocking performance smoke test + baseline measurements) into #190.

This issue (#151) now focuses on the fuller post-1.0 performance program: BenchmarkDotNet, budgets, and CI regression gating.

Motivation

Performance is a stated priority. Need to:

• Measure current performance
• Set acceptable performance budgets
• Detect performance regressions
• Optimize hot paths

Scope

• Benchmark tool execution overhead (target: <100ms)
• Benchmark resource access (template cache, framework info)
• Measure memory usage
• Set up performance tests in CI
• Optimize based on measurements

Success Criteria

• BenchmarkDotNet integration
• Performance budgets defined (<100ms overhead per tool)
• Baseline measurements documented
• CI fails on regression >20%
• Optimization of identified hot paths

Related

• v1.0 slice: #190
• Existing: Template caching already implemented

Start by reviewing the smaller v1.0 slice in #190 and the existing template-caching implementation to understand the current baseline. Define the BenchmarkDotNet scope for tool execution and resource access, then establish memory measurements, budgets, documented baselines, and CI regression gating. Done means the listed success criteria are met, including detecting regressions over 20% and recording any optimizations.