Add persisted filtering (status/priority/tags) to Todo widgets and tests

[multiplex55]

Motivation

• Provide compact, in-widget filter controls (status: all/open/done, minimum priority, tag selector) so users can focus their todo lists without leaving the dashboard.
• Ensure filters are applied before sorting and row rendering so the visible list respects user filters while preserving existing sort/truncate behavior.
• Persist filter state in widget JSON settings so preferences survive restarts and support migration from the legacy show_done flag.

Description

• Added new enums and config fields for filtering: TodoStatusFilter, status, min_priority, and filter_tags to TodoWidgetConfig and analogous TodoFocusStatusFilter and fields to TodoFocusConfig. (files: src/dashboard/widgets/todo.rs, src/dashboard/widgets/todo_focus.rs).
• Implemented compact settings UI controls: status dropdown, min-priority DragValue, and a tag selector populated from the current snapshot; these appear in both the settings UI and the widget header/summary area. (changes in settings_ui and summary rendering).
• Applied composite filtering functions (status_match, priority_match, tags_match, entry_matches_filters) and a filter_entries helper so filtering is executed before sort_entries and truncation, preserving existing sort behavior.
• Added migration helpers (migrate_config) and on_config_updated handlers to translate legacy show_done usage into the new status filter and to normalize tag lists, ensuring backward-compatible persisted config.
• Added unit tests exercising filter composition and JSON round-trip persistence for both widgets: filters_combine_before_sorting and config_serialization_persists_filter_state in todo.rs, and focus_filters_by_status_priority_and_tags and focus_config_persists_filter_state in todo_focus.rs.

Testing

• Ran cargo fmt --all, which completed successfully.
• Attempted cargo test todo_widget -- --nocapture, but the test run failed to build in this environment because the alsa-sys crate requires the system alsa library (alsa.pc via pkg-config) which is not available; therefore the new unit tests could not be executed here.
• The changes compile-formatted cleanly and unit tests are included and should run successfully in an environment with required native dependencies installed.

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Codex Task