@rms >Building all buildings so that they have nothing flammable on the outside would make them safe.
Burning embers tend to find their way into gaps the buildings and light anything flammable inside - you would need to fill in any gaps as well (pretty much impossible to do for tile roof buildings).

>Eliminating all trees would help too.
That would probably make fires worse, as trees have a cooling effect (that slightly mitigates the heating effect of concreting or asphalting everything) and hotter temps mean drier grasses and shrubs.

As far as I can tell, fires are primarily spread by dry grasses and shrubs, as trees require a lot more heat before they start to burn (although in many cases fires were started by tree branches rubbing on powerlines and the resulting sparks ignited the leaves, which then lit up the tree).

It is true that a lot of the fires wouldn't have started if decent maintenance was done on the power distribution network and tree branches that rubbed against power lines were cut.

>Is anyone working on a fire-extinguishing robot? To have 10,000 of those in the LA area would be expensive
It'll be a much better idea to install more fire hydrants and water tanks and keep the tanks full, than to rely on robots that runs proprietary software.