Add tag/priority suffixes to todo add labels

[multiplex55]

Motivation

• Surface parsed tags and priority in the todo add result label so users see the parsed metadata at-a-glance while preserving existing behavior.

Description

• Build a label_suffix_parts list in src/plugins/todo.rs from parsed tags and priority and join parts with ; to produce labels like Add todo testing Tag: testing; priority: 3.
• Keep the action payload format exactly as todo:add:{text}|{priority}|{tag_str} to avoid breaking consumers.
• Update tests/todo_plugin.rs to assert exact labels: search_add_returns_action expects "Add todo task", search_add_with_priority_and_tags expects "Add todo task Tag: a, b; priority: 3", and search_add_with_at_tags expects "Add todo task Tag: a, b".

Testing

• Ran cargo test --test todo_plugin, but the run failed during build due to the missing system alsa library required by alsa-sys (pkg-config could not find alsa.pc), so the unit tests could not complete.
• The label-related unit assertions were added and are ready to run once the build environment provides the alsa system dependency.

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Codex Task