Expand omni search to include notes and todos

[multiplex55]

Motivation

• Aggregate results from notes and todos into the omni (o / o list) pipeline so users see folders, bookmarks, apps, notes and todos in one combined search.
• Separate per-source collection so each source (folders/bookmarks/apps/notes/todos) can preserve its own query semantics and be extended independently.
• Deduplicate combined results to avoid duplicate UX noise while preserving a deterministic result order.
• Preserve the existing apps fast path (FST index with linear fallback) and keep command prefixes unchanged for backward compatibility.

Description

• Added note: NotePlugin and todo: TodoPlugin fields to OmniSearchPlugin and initialized them in OmniSearchPlugin::new(...) alongside folders and bookmarks.
• Refactored search_all to call per-source collectors: collect_folder_results, collect_bookmark_results, collect_app_results, collect_note_results, and collect_todo_results so each source uses its native query form (empty rest → note list / todo list, non-empty rest → note {rest} / todo {rest}).
• Moved app lookup into collect_app_results and preserved the existing FST subsequence search plus the linear fallback when index building fails.
• Added dedup_actions to remove duplicates by a stable key composed of the action string and a normalized, lowercased label while preserving first-seen ordering, and updated description() to reflect the expanded scope.

Testing

• Ran cargo fmt --all, which completed successfully.
• Ran cargo check and cargo check --lib, both of which were blocked by an environment/system dependency error from alsa-sys (missing alsa.pc / pkg-config), so a full build and automated test run could not be completed in this environment.
• No additional automated unit/integration tests were executed due to the build blockage by the missing system pkg-config data.

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Codex Task