Extract all inline code from best_practices.md (9/12)

Created best_practices_patterns.dart with 30+ regions covering:
Architecture patterns:
- logic_in_widget_bad/good
- passing_managers_bad, access_directly_good
- local_ui_state, business_state

Performance:
- watching_too_much_bad, watch_specific_good
- rebuilds_on_every_settings_bad, rebuilds_only_darkmode_good
- one_widget_watches_everything_bad, split_widgets_good_*
- const_constructors
- computing_in_widget_bad, computed_in_manager_good_*

Code organization:
- manager_service_structure
- widget_structure

Common patterns:
- master_detail_navigation
- pull_to_refresh_pattern
- search_filter_pattern
- pagination_pattern

Anti-patterns:
- dont_access_getit_constructors_good
- dont_violate_ordering_bad
- dont_await_execute_bad/good_anti

Debugging:
- enable_tracing, log_watch_calls, check_rebuild_frequency

All code blocks extracted from best_practices.md.
Examples compile successfully (32 info warnings only).

Progress: 9 files done, 3 remaining.

Author: escamoteur