M1: PHPUnit test suite for crypto, repository and resumable runs

Dev tooling via composer (phpunit, psalm, nextcloud/ocp); vendor/ is
mounted from outside the repository by a helper script. 28 unit tests
ported from the phase-0 spikes (round trips, corruption, wrong keys,
dedup, incremental runs, partial restore, tampering, object binding,
time-boxed steps, file changed between steps).

composer.json

@@ -0,0 +1,34 @@
+{
+	"name": "dillardblom/ng_backup",
+	"description": "NG Backup: encrypted, incremental Nextcloud backups",
+	"license": "AGPL-3.0-or-later",
+	"type": "project",
+	"autoload": {
+		"psr-4": {
+			"OCA\\NgBackup\\": "lib/"
+		}
+	},
+	"autoload-dev": {
+		"psr-4": {
+			"OCA\\NgBackup\\Tests\\": "tests/"
+		}
+	},
+	"require": {
+		"php": ">=8.1"
+	},
+	"require-dev": {
+		"phpunit/phpunit": "^10.5",
+		"nextcloud/ocp": "dev-stable32",
+		"vimeo/psalm": "^6.0"
+	},
+	"config": {
+		"optimize-autoloader": true,
+		"platform": {
+			"php": "8.2.27"
+		}
+	},
+	"scripts": {
+		"test:unit": "phpunit -c tests/phpunit.xml --testsuite unit",
+		"psalm": "psalm --no-cache --threads=1"
+	}
+}