feat: add AWS Lambda Managed Instances (LMI) skill to aws-serverless plugin

[sbbhimji]

Summary

Adds a new skill to help users evaluate, configure, and migrate workloads to AWS Lambda Managed Instances (LMI) — the
recently launched feature that runs Lambda functions on dedicated EC2 instances with AWS managing the lifecycle.

What's included

SKILL.md (205 lines) — core workflow with 6 steps:

1. Workload fitness assessment (decision table: LMI vs standard Lambda)
2. 4-column cost comparison (Lambda OD, Lambda+SP, LMI OD, LMI+3yr SP)
3. Configuration recommendations (instance types, memory ratios, concurrency)
4. Code migration for multi-concurrency thread safety
5. Infrastructure setup (IAM, VPC, capacity providers)
6. Validation and gradual production cutover

6 reference files (42-96 lines each):

• cost-comparison.md — pricing formulas, discount comparison, worked example, break-even guidance
• configuration-guide.md — instance type decision tree, memory sizing from existing Lambda/EC2, concurrency tuning,
  scaling controls
• thread-safety.md — code review checklist, runtime-specific guidance (Node.js, Python, Java, .NET), common
  anti-patterns
• migration-patterns.md — before/after code examples per runtime (global state, file I/O, database connections)
• infrastructure-setup.md — IAM roles, VPC requirements, CLI workflow, SAM template
• troubleshooting.md — common issues, debugging steps for startup/performance/cost

Plugin registration:

• Added managed-instances and lmi keywords to plugin.json
• Added LMI skill triggers to README aws-serverless section
• Added cross-references in aws-lambda/SKILL.md (Key Capabilities + When to Load Reference Files)

Design decisions

• 4-column cost comparison includes Lambda with Savings Plans (not just on-demand) since customers often already have
  Compute Savings Plans covering Lambda duration
• Thread safety is the critical migration gate — elevated to its own reference file with a per-runtime checklist since
  this is the feat: initial branch #1 source of production issues when adopting LMI
• Follows all plugin standards: SKILL.md under 300 lines, reference files under 100 lines, proper frontmatter,
  progressive disclosure, explicit defaults, error handling

Test plan

• Load plugin locally: claude --plugin-dir ./plugins/aws-serverless
• Verify skill auto-triggers on "is LMI right for my workload?"
• Verify skill auto-triggers on "migrate my Lambda to managed instances"
• Verify cost comparison produces 4-column table (Lambda OD / Lambda+SP / LMI OD / LMI+SP)
• Verify thread-safety checklist surfaces when reviewing function code
• Verify cross-reference from aws-lambda skill routes to LMI skill
• Confirm SKILL.md < 300 lines, all reference files < 100 lines
• Run claude --plugin-dir ./plugins/aws-serverless --verbose to verify < 5000 token initial load

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