feat(backend): local accounts + invites for Gemeinde Teamer

Per the updated plan, Gemeinde Teamer are no longer Authentik-backed; they
are local accounts a Gemeinde Verantwortliche/r provisions per KC.

Schema:
- User.authentikSub now nullable; add passwordHash + kcId (cascade from Kc)
  so one User model covers Authentik members and local Teamer.
- new TeamerInvite model: shareable group link (email null, maxUses null)
  or personal invite (email pinned, single use), with expiry + revoke.
- sync log now also replicates User / Membership / TeamerInvite.

Auth:
- TeamAuthService: bcrypt password login (POST /auth/team-login) and invite
  redemption (POST /auth/teamer/register) issuing a JWT signed with
  TEAM_JWT_SECRET, payload typ:"team".
- TeamJwtStrategy (AuthGuard('team')) resolves it to the same
  AuthenticatedUser shape as AuthentikStrategy.
- TokenVerificationService.verifyEither() also accepts team tokens (WS).
- files + chat read endpoints accept 'team' tokens; Teamer see non-Konfi
  files and can use chat / start DMs.

Teamer admin (teamer/ module, under /gemeinde/:gemeindeId):
- POST/GET teamer, DELETE teamer/:userId
- POST/GET teamer-invites, DELETE teamer-invites/:inviteId
- LT may manage any Gemeinde; a Verantwortliche/r only their own
  (checked in TeamerService, since RolesGuard only scopes by kcId).

Tests: TeamAuthService + TeamerService specs added (Prisma/Sync mocked),
npm test green at 32. Docs (plan + backend README) updated.

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

package-lock.json

@@ -21,6 +21,7 @@
         "@nestjs/serve-static": "^4.0.2",
         "@nestjs/websockets": "^10.4.15",
         "@prisma/client": "^5.22.0",
+        "bcryptjs": "^3.0.3",
         "class-transformer": "^0.5.1",
         "class-validator": "^0.14.1",
         "jsonwebtoken": "^9.0.2",
@@ -37,6 +38,7 @@
         "@nestjs/cli": "^10.4.9",
         "@nestjs/schematics": "^10.2.3",
         "@nestjs/testing": "^10.4.15",
+        "@types/bcryptjs": "^2.4.6",
         "@types/express": "^4.17.21",
         "@types/jest": "^29.5.14",
         "@types/jsonwebtoken": "^9.0.7",
@@ -2776,6 +2778,13 @@
         "@babel/types": "^7.28.2"
       }
     },
+    "node_modules/@types/bcryptjs": {
+      "version": "2.4.6",
+      "resolved": "https://registry.npmjs.org/@types/bcryptjs/-/bcryptjs-2.4.6.tgz",
+      "integrity": "sha512-9xlo6R2qDs5uixm0bcIqCeMCE6HiQsIyel9KQySStiyqNl2tnj2mP3DX1Nf56MD6KMenNNlBBsy3LJ7gUEQPXQ==",
+      "dev": true,
+      "license": "MIT"
+    },
     "node_modules/@types/body-parser": {
       "version": "1.19.6",
       "resolved": "https://registry.npmjs.org/@types/body-parser/-/body-parser-1.19.6.tgz",
@@ -3923,6 +3932,15 @@
         "node": ">=6.0.0"
       }
     },
+    "node_modules/bcryptjs": {
+      "version": "3.0.3",
+      "resolved": "https://registry.npmjs.org/bcryptjs/-/bcryptjs-3.0.3.tgz",
+      "integrity": "sha512-GlF5wPWnSa/X5LKM1o0wz0suXIINz1iHRLvTS+sLyi7XPbe5ycmYI3DlZqVGZZtDgl4DmasFg7gOB3JYbphV5g==",
+      "license": "BSD-3-Clause",
+      "bin": {
+        "bcrypt": "bin/bcrypt"
+      }
+    },
     "node_modules/binary-extensions": {
       "version": "2.3.0",
       "resolved": "https://registry.npmjs.org/binary-extensions/-/binary-extensions-2.3.0.tgz",