Cleanup: remove dead auth middleware and fix security log leak

- Remove dead AdminOnly() and AdminTokenAuth() middleware (unused since JWT switch)
- Remove dead RequireScope() middleware (also unused)
- Fix seed.go: only log password when auto-generated (was logging every time)
- Fix seed.go: use admin.Username (normalized) instead of raw username in log
- Simplify generateRandomPassword: 12 bytes (24 hex chars) instead of 24 bytes then truncate
- Me handler: use claims.Subject (UUID) for lookup instead of username
- Remove unused /logout endpoint (stateless JWT)

internal/api/handlers/admin/login.go

@@ -66,6 +66,4 @@ func (h *LoginHandler) Login(c *gin.Context) {
 	})
 }
 
-func (h *LoginHandler) Logout(c *gin.Context) {
-	c.Status(http.StatusOK)
-}
+