Normalize local usernames to lowercase

Normalize local account usernames by trimming and lowercasing across the stack. Added a Prisma migration to lowercase existing plex_username and rewrite local plex_id values for non-deleted accounts. Updated LocalAuthProvider, admin login route, and setup completion to use normalized usernames when looking up, creating, and storing users (including plexId `local-{username}`). Added/updated tests to assert case-insensitive lookups, storage of lowercased usernames/plexIds, and duplicate username rejection.

src/lib/services/auth/LocalAuthProvider.ts

@@ -54,10 +54,12 @@ export class LocalAuthProvider implements IAuthProvider {
         return { success: false, error: 'Username and password required' };
       }
 
+      const normalizedUsername = username.trim().toLowerCase();
+
       // Find user (exclude soft-deleted users)
       const user = await prisma.user.findFirst({
         where: {
-          plexUsername: username,
+          plexUsername: normalizedUsername,
           authProvider: 'local',
           deletedAt: null, // Exclude soft-deleted users
         },
@@ -144,9 +146,10 @@ export class LocalAuthProvider implements IAuthProvider {
   async register(params: RegisterParams): Promise<AuthResult> {
     try {
       const { username, password } = params;
+      const normalizedUsername = username?.trim().toLowerCase();
 
       // Validate
-      if (!username || username.length < 3) {
+      if (!normalizedUsername || normalizedUsername.length < 3) {
         return { success: false, error: 'Username must be at least 3 characters' };
       }
 
@@ -167,7 +170,7 @@ export class LocalAuthProvider implements IAuthProvider {
       // Check username uniqueness (only among non-deleted users)
       const existing = await prisma.user.findFirst({
         where: {
-          plexUsername: username,
+          plexUsername: normalizedUsername,
           authProvider: 'local',
           deletedAt: null, // Allow reuse of usernames from deleted accounts
         },
@@ -194,8 +197,8 @@ export class LocalAuthProvider implements IAuthProvider {
       // Create user
       const user = await prisma.user.create({
         data: {
-          plexId: `local-${username}`,
-          plexUsername: username,
+          plexId: `local-${normalizedUsername}`,
+          plexUsername: normalizedUsername,
           authToken: encryptedHash,
           authProvider: 'local',
           role: isFirstUser ? 'admin' : 'user',