feat: add parse endpoint, refactor recurring tasks, and improve web task completion

Extract CreateRecurringTask into engine package for reuse by both CLI
and API. Add POST /tasks/parse endpoint for CLI-style input parsing.
Remove FK constraint on change_log to preserve history after task
deletion. Update web frontend to filter completed tasks from view and
add mock mode support for development.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

opal-web/src/lib/components/ReportPicker.svelte

@@ -9,11 +9,6 @@
 	 */
 	export let onSelect;
 
-	/**
-	 * @type {HTMLElement}
-	 */
-	export let anchorEl;
-
 	/** @type {HTMLElement|null} */
 	let popoverEl = null;