My cleric can"t cast his first lvl spells. I've ried stripping his armor and his 1st lvl spells are greyed out.

Did you select which spells to use in spellbook (B) and then rest to learn them?

Armor does not affect divine (cleric) magic. You have to open spell book, select spells to memorise and then rest to "charge" them. Other reason for not casting may be "Fatigue", it makes fatigued character unable to use skills and spells are treated as skills. Again only way to get rid of fatigue is resting.

Does your cleric have at least 11 wisdom?

Spellcasting requires certain mental stats (int wis cha) to cast.

Wisdom is 19. I've rested, LN align, Torag diety. Spells are in hotkeys, but greyed out.

Tristian has cleric spellcasting blocked by using some armors, while the dwarf was able to cast anything in full plate. I think you just need to remove your armor.
I think it is a matter of some feat, that allow you to cast cleric spells while using armor.

Did you memorise the same spells You have in hotkeys bar?

It is the type of Cleric Tristian is (Ecclesitheurge) which restricts him casting with armor. Any other type of cleric can cast in armor by default.

I think it's an alignment bug. LN isn't sync'd with Torag properly. I've rebuilt the character as LG and everything works fine.

It does not prevent him from casting in armor. He just does not posses armor proficiency. Just checked. Tristian class crossed with e.g. fighter can cast his spells even in plate armor, same if you take an armor proficiencies on levelups (checked only for ight and medium did not get far enought to check for heavy) he can cast spells in them.