LF: rank buildings and researches by payback time across celestials

The bot already knows every input needed to rank LF investments: current levels per celestial, costs, and production output. What is missing is the ranking itself.

Third-party tools do this and it is the main reason people run them alongside the bot. A typical row looks like:

Catalyser Technology 0 -> 1
cost 20,900 MSU
gain +1,650 MSU/h
payback 4h13m

Sorted by payback time, this immediately shows that a level 0 -> 1 on ten celestials beats a level 4 -> 5 on one, because LF research levels are per-celestial while the effect is global.

Suggested change: a view listing candidate LF buildings and researches across all celestials, with cost, hourly gain and payback time, sorted by payback. Optionally a button to push the top entries into Brain ceilings.

This would also make artifact spending decisions concrete, since a paid slot costs 400 artifacts and there is currently no way to compare where that is best spent.