you can modify the capship and ship count .entities. they should look something like
RESEARCHSUBJECT_MAXCAPITALSHIPSTECH0.entity
RESEARCHSUBJECT_MAXCAPITALSHIPSTECH1.entity
RESEARCHSUBJECT_MAXCAPITALSHIPSTECH2.entity
etc.
RESEARCHSUBJECT_MAXSHIPSLOTSPHASE0.entity
RESEARCHSUBJECT_MAXSHIPSLOTSPHASE1.entity
RESEARCHSUBJECT_MAXSHIPSLOTSPHASE2.entity
etc.
a word of warning tho, it WILL get lagy and the AI WILL max it out, generally in 1 massive fleet. you can also modify the ship upkeep in the ship slot files.
NOTE: you got to use the text formats of the files, generaly found in the forge tools released for that version. the newest version as well as entrenchment dont have tools out yet i dont believe but there is a topic on the changes and converting some of the files, although that does not apply for the new version of entrenchment i dont believe.