feat: add CloudFormation resource count warning

[hoegertn]

Description

Reimplements #158 with improvements based on the feedback from the previous attempt in PR #172.

This PR adds a CloudFormation resource counting feature that monitors resource usage across stacks during CDK synthesis and warns when approaching the 500 resource limit.

Changes

New Files

• src/awscdk/count-resources.ts — Standalone CLI tool that parses the cloud assembly's manifest.json, counts resources per stack, and outputs results to console, JSON file, and optionally GitHub step summary
• src/awscdk/resource-count-step.ts — ResourceCountStep pipeline step wrapping the CLI call
• test/count-resources.test.ts — Unit tests for the resource counter logic
• test/resource-count-github.test.ts — Integration tests for GitHub pipeline
• test/resource-count-gitlab.test.ts — Integration tests for GitLab pipeline

Modified Files

• src/awscdk/base.ts — Adds configuration options and provideResourceCountStep() to base class
• src/awscdk/github.ts — Integrates resource counting into existing synth job with PR comment support
• src/awscdk/gitlab.ts — Integrates resource counting into existing synth job with MR comment support
• src/awscdk/index.ts — Exports new module
• .projenrc.ts — Adds count-resources bin entry

Configuration

new GithubCDKPipeline(this, {
  enableResourceCounting: true,        // default: true
  resourceCountWarningThreshold: 450,  // default: 450
  resourceCountLimit: 500,             // default: 500 (configurable for accounts with increased limits)
});

Improvements over PR #172

1. No redundant synth — Resource counting runs in the existing synth job rather than a separate workflow
2. Delta tracking — On PRs, checks out the baseline from the target branch and reports resource count changes
3. Configurable hard limit — resourceCountLimit option (default 500) for accounts with increased quotas
4. GitLab MR support — Posts resource count summaries to GitLab merge requests via Notes API
5. Robust CI behavior — Uses || true so the step does not fail the pipeline; results are always reported

Test Results

• 17 unit tests for ResourceCounter CLI logic
• 3 GitHub integration tests (enabled/disabled/custom limits)
• 2 GitLab integration tests (enabled/disabled)
• All tests pass

Closes #158

[hoegertn]

@kiro-agent Where does this file come from in the repo. Where is it committed? It should not be stored