fix: never allow the projects directory to become a project directory

Loading a .gns3 placed directly in the projects root registered the
shared projects directory as the project path (load_project derives
the path from the file's parent directory). Deleting such an entry ran
rmtree on the projects directory itself, wiping every project until a
root-owned file stopped it, and left a zombie entry in the controller.

Three layers of protection:

- Controller.load_project() refuses a .gns3 whose parent directory is
  the projects directory; the normal subdirectory layout is unaffected
- the Project.path setter rejects the projects directory itself and
  its ancestors, closing the same hole for POST/PUT with an explicit
  path
- Project.delete() uses realpath + commonpath instead of commonprefix:
  entries whose path is the projects root are refused, and sibling
  directories sharing a string prefix (/srv/projects-evil vs
  /srv/projects) are no longer treated as inside the projects dir

Also removes the project_load MCP tool: loading by raw server
filesystem path is a footgun for automated clients; projects can still
be opened by project_id via the remaining tools.

gns3server/controller/project.py

@@ -471,6 +471,18 @@ class Project:
     @path.setter
     def path(self, path):
         check_path_allowed(path)
+
+        # The projects directory itself (or one of its ancestors) must
+        # never become a project directory: deleting such a "project"
+        # would wipe every project on the controller.
+        real_path = os.path.realpath(path)
+        real_projects_path = os.path.realpath(get_default_project_directory())
+        if os.path.commonpath([real_path, real_projects_path]) == real_path:
+            raise ControllerForbiddenError(
+                f"The project directory cannot be '{path}': it must be a subdirectory "
+                f"of '{real_projects_path}', not the projects directory itself or one of its parents"
+            )
+
         try:
             os.makedirs(path, exist_ok=True)
         except OSError as e:
@@ -1608,11 +1620,19 @@ class Project:
         await self._cleanup_web_wireshark_container()
 
         try:
-            project_directory = get_default_project_directory()
-            if not os.path.commonprefix([project_directory, self.path]) == project_directory:
+            project_directory = os.path.realpath(get_default_project_directory())
+            path = os.path.realpath(self.path)
+            if os.path.commonpath([path, project_directory]) != project_directory:
                 raise ControllerError(
                     f"Project '{self._name}' cannot be deleted because it is not in the default project directory: '{project_directory}'"
                 )
+            if path == project_directory:
+                # A poisoned or hand-crafted entry whose path is the
+                # projects root itself must never be deletable: rmtree
+                # would wipe every project on the controller.
+                raise ControllerError(
+                    f"Project '{self._name}' cannot be deleted because its directory is the projects directory itself: '{path}'"
+                )
             shutil.rmtree(self.path)
         except OSError as e:
             raise ControllerError(f"Cannot delete project directory {self.path}: {str(e)}")