test: AuthLog-Regressionstests (wirft nie, 500-Zeilen-Kappung)

AuthLog.write ist der einzige Aufruf im catch-Pfad des Soft-Logout-Guards;
ein Throw dort würde im SDK zu logout()+clear() eskalieren. 4 neue Tests
sichern genau das ab (kaputte Plattform, leeres Log, Zeitstempel, Kappung).
path_provider_platform_interface als dev_dependency (war schon transitiv).
Alle 14 Tests grün auf dem Pi, flutter analyze unverändert.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

pubspec.lock

@@ -801,10 +801,10 @@ packages:
     dependency: transitive
     description:
       name: meta
-      sha256: "23f08335362185a5ea2ad3a4e597f1375e78bce8a040df5c600c8d3552ef2394"
+      sha256: "1741988757a65eb6b36abe716829688cf01910bbf91c34354ff7ec1c3de2b349"
       url: "https://pub.dev"
     source: hosted
-    version: "1.17.0"
+    version: "1.18.0"
   mime:
     dependency: "direct main"
     description:
@@ -918,7 +918,7 @@ packages:
     source: hosted
     version: "2.2.1"
   path_provider_platform_interface:
-    dependency: transitive
+    dependency: "direct dev"
     description:
       name: path_provider_platform_interface
       sha256: "88f5779f72ba699763fa3a3b06aa4bf6de76c8e5de842cf6f29e2e06476c2334"
@@ -1294,18 +1294,18 @@ packages:
     dependency: transitive
     description:
       name: test_api
-      sha256: "8161c84903fd860b26bfdefb7963b3f0b68fee7adea0f59ef805ecca346f0c7a"
+      sha256: "949a932224383300f01be9221c39180316445ecb8e7547f70a41a35bf421fb9e"
       url: "https://pub.dev"
     source: hosted
-    version: "0.7.10"
+    version: "0.7.11"
   test_core:
     dependency: transitive
     description:
       name: test_core
-      sha256: "0381bd1585d1a924763c308100f2138205252fb90c9d4eeaf28489ee65ccde51"
+      sha256: "1991d4cfe85d5043241acac92962c3977c8d2f2add1ee73130c7b286417d1d34"
       url: "https://pub.dev"
     source: hosted
-    version: "0.6.16"
+    version: "0.6.17"
   timezone:
     dependency: transitive
     description: