Add performance benchmarking and set performance budgets

[jongalloway]

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: Performance smoke test + baseline measurements (v1.0) #190
• Existing: Template caching already implemented