feat(tests): implement test reliability improvements (Tasks 24-27)

BREAKING CHANGE: Tests now fail loudly when dependencies are missing

- Remove all conditional test skips enforcing "fail loudly" philosophy
- Add test filtering capabilities for CI environments
  - test:no-python - skip Python-dependent tests
  - test:no-docker - skip Docker-dependent tests  
  - test:ci - alias for test:no-docker
- Refactor session manager for multi-language support
  - Generic executable path resolution (not Python-specific)
  - Better error handling and logging
- Update mock adapter with improved process handling
- Remove obsolete tests and temporary files
  - Deleted session-manager-backup.ts (temporary recovery)
  - Removed python-real-discovery.test.ts (redundant)
  - Removed path-resolution.test.ts (obsolete)
- Add comprehensive documentation for test improvements
- Fix container test reliability with proper cleanup

All 808 tests now pass without skips when dependencies are available.

Philosophy: Tests explicitly fail when dependencies are missing rather than
being silently skipped. Use test:no-python or test:no-docker scripts only
in CI environments where specific dependencies are unavailable.

Refs: Tasks 24, 25, 26, 27
