Add documentation for state tracking, progress monitoring, and result persistence

Documents features added in PRs #181, #184, and #189:

- Add comprehensive "Task State and Progress Monitoring" section to advanced-patterns.md
  covering execution state machine, Redis data model, pub/sub events, progress reporting,
  result retrieval, and CLI monitoring

- Add Progress() dependency documentation to dependencies.md with usage examples
  and links to detailed patterns

- Add "State and Result Storage" section to production.md documenting execution_ttl
  configuration, fire-and-forget mode (execution_ttl=0), and custom result storage backends

- Add "Task Observability" section to getting-started.md introducing state tracking,
  progress reporting, and result retrieval with links to detailed documentation

All documentation includes working code examples and follows the existing tone and style.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: desertaxle