[MMMikeM]

Search across every list, done tasks, subtasks, descriptions and notes, as approved in the mock-up. It runs on the device, so it works offline, and matches with Ekrina.

• Desktop: a Search row at the top of the sidebar; / opens it unless something is being typed (the empty capture input doesn't count) or a sheet is open.
• Phone: a "Search all lists" field at the top of the lists sheet. It's a button that holds the keyboard up across the page change (lib/keyboard-bridge.ts), which needs checking on a real iPhone.
• Results group by list in the sidebar's order, then Done with each task's list and completion date. A description or note match shows its line; a subtask shows its parent. A typo shows "Showing results for …".
• Add puts the query in the list search was opened from, unless a task already has that title or the query was corrected.
• Opening a result sheets it over the results; closing keeps the query.

Also moves the toast viewport to the root: it only existed on the list page, so toasts from People (and now search) were never shown.

Based on #11 (it needs completedAt and soft-deleted tasks kept out). Once #11 merges, this rebases onto main.