feat: improve session naming with workspace-aware scoped numbering

When a workspace is provided, auto-generated display names now use
workspace.name instead of repo.name:
  'myworkspace / VS Code Server'          # first
  'myworkspace / VS Code Server #2'       # second

Without a workspace, naming falls back to repo.name:
  'myrepo / VS Code Server'
  'myrepo / VS Code Server #2'

The counter is scoped to workspace+tool_type (or repo+tool_type),
so different tool types for the same workspace/repo are numbered
independently.

This replaces the old format of 'project / repo / tool #N' which
was always repo-based and included the project name even though
the sidebar already groups by project.

Quality gates: py_compile passed, ruff passed.

apps/api/src/api/tool/tool_instances.py

@@ -853,19 +853,31 @@ async def create_instance(
         # Generate unique name
         instance_name = f"{tool_type.name}-{repo.name}-{uuid.uuid4().hex[:8]}"
 
-        # Auto-generate display name with numbering when duplicates exist
+        # Auto-generate display name with scoped numbering.
+        # When a workspace is provided, use workspace name + tool type.
+        # Otherwise fall back to repo name + tool type.
         if data.display_name:
             instance_display = data.display_name
         else:
-            auto_name = f"{_project.name} / {repo.name} / {tool_type.display_name}"
-            result = await session.execute(
-                select(ToolInstance).where(
-                    ToolInstance.project_id == project_id,
-                    ToolInstance.repository_id == repo_id,
-                    ToolInstance.tool_type_id == tool_type_id,
-                    ToolInstance.owner_id == user_id,
+            scope_name = workspace.name if workspace else repo.name
+            auto_name = f"{scope_name} / {tool_type.display_name}"
+
+            if workspace:
+                count_query = (
+                    select(ToolInstance)
+                    .where(ToolInstance.workspace_id == workspace_id)
+                    .where(ToolInstance.tool_type_id == tool_type_id)
+                    .where(ToolInstance.owner_id == user_id)
                 )
-            )
+            else:
+                count_query = (
+                    select(ToolInstance)
+                    .where(ToolInstance.repository_id == repo_id)
+                    .where(ToolInstance.tool_type_id == tool_type_id)
+                    .where(ToolInstance.owner_id == user_id)
+                )
+
+            result = await session.execute(count_query)
             existing_count = len(result.scalars().all())
             if existing_count > 0:
                 instance_display = f"{auto_name} #{existing_count + 1}"