feat: dashboard widget (#18), differential backups (#19), JPA import (#20)

#18 — Dashboard Quickicon Widget:
- plg_quickicon_mokobackup: shows backup status on admin dashboard
- Displays: last backup time, total count, storage used
- Warning states: no backups, recent failures, stale (>7 days)
- Links to backup records view

#19 — Differential Backups:
- New backup_type: "differential" — only backs up changed/new files
- DifferentialScanner: builds manifest (path+size+mtime) on full backups
- Compares current filesystem against base manifest on differential runs
- Manifest stored in backup record (LONGTEXT column)
- Falls back to full backup if no base manifest exists
- Database is always fully dumped (no incremental DB)

#20 — JPA Format Import:
- JpaUnarchiver: parses Akeeba JPA binary format
- Handles: archive header, file entities, gzip decompression, permissions
- RestoreEngine auto-detects JPA vs ZIP by reading signature bytes
- Enables restoring from existing Akeeba .jpa backup files

Authored-by: Moko Consulting
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/script.php

@@ -74,6 +74,17 @@ class Pkg_MokoBackupInstallerScript
 			$db->setQuery($query);
 			$db->execute();
 
+			// Enable the quickicon plugin automatically
+			$query = $db->getQuery(true)
+				->update($db->quoteName('#__extensions'))
+				->set($db->quoteName('enabled') . ' = 1')
+				->where($db->quoteName('type') . ' = ' . $db->quote('plugin'))
+				->where($db->quoteName('folder') . ' = ' . $db->quote('quickicon'))
+				->where($db->quoteName('element') . ' = ' . $db->quote('mokobackup'));
+
+			$db->setQuery($query);
+			$db->execute();
+
 			// Enable the task plugin automatically
 			$query = $db->getQuery(true)
 				->update($db->quoteName('#__extensions'))