Add deployment flow and health check documentation - #7

Adds operational documentation for extension publishing and monitoring.

Changes

• docs/deployment-flow.md: Complete deployment guide covering build process, packaging with vsce, Marketplace publishing, version management, rollback procedures, and CI/CD integration
• docs/health-check.md: Monitoring and verification procedures including activation checks, command registration validation, performance metrics, error tracking, and incident response protocols
• README.md: Added documentation section linking to new guides

Key Coverage

Deployment flow includes:

• Local development setup and testing workflow
• Version management and changelog practices
• Package validation and testing procedures
• Marketplace publishing (manual and automated)
• Rollback strategies for critical issues

Health checks include:

• Extension activation and command registration verification
• Functional test scenarios with expected outputs
• Performance targets (activation <100ms, commands <50ms)
• Error tracking and logging recommendations
• Daily/weekly/monthly monitoring checklists

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