feat: adds doctor preflight checks.

[karlzierhofer]

Why

Improve preflight diagnostics and first-run resilience, and keep configuration rendering deterministic by resolving required values during init instead of mutating rendered config during deploy.
In addition, document the overlapping-pipeline commit race clearly while waiting for an upstream LZA fix.

What

• Added a doctor preflight command with actionable output.
• deploy runs doctor automatically and aborts on failures (--skip-doctor available).
• Added fixture mode for offline doctor output reproduction.
• Added a quotas command to request Lambda concurrency quota increases (--dry-run supported, skips already pending requests).
• Moved Control Tower CloudTrail log group resolution to init and rendered it directly into config output.
• Added init prechecks to validate rollout readiness (including finalize marker checks with region fallback behavior).
• Added/updated regression tests for init, doctor, and deploy failure paths.
• Added detailed runbook documentation for the overlapping execution commit-race analysis and linked it from common issues.

Doctor checks

• AWS account matches managementAccountId
• Installer version (SSM) matches awsAcceleratorVersion
• Installer stack exists
• Config bucket exists
• CDK assets buckets exist for all enabledRegions
• Lambda concurrency meets minLambdaConcurrency across enrolled accounts/regions
• LZA checkout exists and branch matches awsAcceleratorVersion