Suggestions:
1. Add a confirmation for reseting the game.
2. Add space as an alternative to right click for laptop users.
3. Don't allow to shoot or plant with just one orb left.
3.5 If all members of the party have healing and the sum of their total healing equals the enemies sum of attack minus the front hero armor times enemies,then the front hero should attack instead of healing.
Sorry, if this sounds commanding but I tried to formulate all these mechanics as "If...then..." sentences so it's easier to translate them into code.
A few suggestions for the AI:
1. If the healer is the last remaining member of the party and their healing ability equals the sum of the enemies attack power minus armor times enemies, then make that they don't heal to avoid loops.
2. If the current target enemy can be killed by the healer in one hit without risking that the current front hero gets killed, than make them attack instead of healing.
3. For the current healing AI, the healer stops healing as soon as their healing ability is smaller than the enemies attack sum minus front hero armor times enemies. However, if the healer is not the only party member, then they should only stop healing if the sum of all the healers ability that can still act in this round and the remaining HP of the front hero are smaller than the attack sum of the enemies minus the front hero armor times enemies. Or, in other words, if healing the front hero wouldn't give them a chance to attack again.
I would suggest an upgrade archive where you can see all the upgrades you have unlocked so far in past resets and maybe show some hints for undiscovered ones. It is barely possible to remember all the upgrades and when they unlock.