fix: ensure context_get applies pagination defaults consistently

- Added validation of pagination parameters at handler level
- Default limit of 100 now properly applied when not specified
- Invalid limit/offset values validated and fallback to defaults
- Response includes defaultsApplied metadata
- Added comprehensive tests for pagination behavior
- Updated API documentation with pagination defaults

This ensures consistent behavior across all paginated endpoints and
prevents potential token limit issues with large result sets.

Author: mkreyman