feat(auth): split inventory scope out of server scope

Carve a new nezha:inventory:{read,delete,*} resource family out of
nezha:server:*. Listing and deleting servers/server-groups (GET /server,
/server-group, /ws/server, batch-delete/server[-group], MCP server.list)
now require nezha:inventory:*, while nezha:server:* covers per-server
runtime operations (get, exec, fs, config, metrics, batch-move,
force-update).

Also declare MCP tool OutputSchema for exec/fs/meta/server/transfer and
wrap server.list output in {servers,count} so strict MCP clients accept
the structured result. Correct the /file all-of scope entry and the stale
server:read documentation.

cmd/dashboard/controller/mcp_sdk_compat_test.go

@@ -53,6 +53,8 @@ func setupSDKCompat(t *testing.T) (string, string, func()) {
 	srv.SetTaskStream(&e2eStream{dispatch: agentSim})
 
 	_, plain := mkToken(t, uid, []string{
+		model.ScopeInventoryRead,
+		model.ScopeInventoryDelete,
 		model.ScopeServerRead,
 		model.ScopeServerWrite,
 		model.ScopeServerDelete,