feat(account): Login, Registrierung, Passwort zurücksetzen

- appwrite 22.4.1 (exakt gepinnt); Client mit Endpoint aus VITE_APPWRITE_ENDPOINT
  bzw. location.origin + /v1, Projekt aus VITE_APPWRITE_PROJECT_ID bzw. aircard
- auth.ts: getCurrentUser (401 -> null, ungültige Antwort -> Fehler), login, register,
  logout, Passwort-Link anfordern/abschließen, onAuthChange, validatePassword
- errors.ts: deutsche Meldungen nach type, dann code (Tabelle aus dem Plan)
- Login-Dialog (Anmelden/Registrieren/Passwort vergessen) als gemeinsames <dialog>,
  Konto-Menü im Seitenkopf, Seite /passwort-neu
- Tests: errors, auth, Dialog, Passwort-neu-Seite

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/package-lock.json

@@ -8,7 +8,8 @@
       "name": "aircard-web",
       "version": "0.1.0",
       "dependencies": {
-        "@fontsource-variable/nunito-sans": "5.3.0"
+        "@fontsource-variable/nunito-sans": "5.3.0",
+        "appwrite": "22.4.1"
       },
       "devDependencies": {
         "happy-dom": "20.14.5",
@@ -434,6 +435,15 @@
         "url": "https://opencollective.com/vitest"
       }
     },
+    "node_modules/appwrite": {
+      "version": "22.4.1",
+      "resolved": "https://registry.npmjs.org/appwrite/-/appwrite-22.4.1.tgz",
+      "integrity": "sha512-NlEgUvSo7A1m+TEHZ8zlWUIuCDtNg3VN6Mbxd6r+1618CiWokig630FpeKQ9/WD5Io92QxuTV/dVzBLPlQghqg==",
+      "license": "BSD-3-Clause",
+      "dependencies": {
+        "json-bigint": "1.0.0"
+      }
+    },
     "node_modules/assertion-error": {
       "version": "2.0.1",
       "resolved": "https://registry.npmjs.org/assertion-error/-/assertion-error-2.0.1.tgz",
@@ -444,6 +454,15 @@
         "node": ">=12"
       }
     },
+    "node_modules/bignumber.js": {
+      "version": "9.3.1",
+      "resolved": "https://registry.npmjs.org/bignumber.js/-/bignumber.js-9.3.1.tgz",
+      "integrity": "sha512-Ko0uX15oIUS7wJ3Rb30Fs6SkVbLmPBAKdlm7q9+ak9bbIeFf0MwuBsQV6z7+X768/cHsfg+WlysDWJcmthjsjQ==",
+      "license": "MIT",
+      "engines": {
+        "node": "*"
+      }
+    },
     "node_modules/buffer-image-size": {
       "version": "0.6.4",
       "resolved": "https://registry.npmjs.org/buffer-image-size/-/buffer-image-size-0.6.4.tgz",
@@ -569,6 +588,15 @@
         "node": ">=20.0.0"
       }
     },
+    "node_modules/json-bigint": {
+      "version": "1.0.0",
+      "resolved": "https://registry.npmjs.org/json-bigint/-/json-bigint-1.0.0.tgz",
+      "integrity": "sha512-SiPv/8VpZuWbvLSMtTDU8hEfrZWg/mH/nV/b4o0CYbSxu1UIQPLdwKOCIyLQX+VIPO5vrLX3i8qtqFyhdPSUSQ==",
+      "license": "MIT",
+      "dependencies": {
+        "bignumber.js": "^9.0.0"
+      }
+    },
     "node_modules/lightningcss": {
       "version": "1.33.0",
       "resolved": "https://registry.npmjs.org/lightningcss/-/lightningcss-1.33.0.tgz",