Heads of staff PDAs start with twice as much disk space (#84874)

## About The Pull Request

Title. Makes heads' and captain's PDAs have 128 GQ of memory instead of
only 64.

## Why It's Good For The Game
RD and CE's PDAs are completely filled roundstart, and while its not
critical for CE, RD needs to delete at least two apps in order to be
able to submit gas shell experiments which is extremely annoying. Other
heads of staff PDAs have been upgraded for parity.

## Changelog
🆑
qol: Heads of staff PDAs start with twice as much disk space
/🆑

---------

Co-authored-by: Zephyr <12817816+ZephyrTFA@users.noreply.github.com>

code/modules/modular_computers/computers/item/role_tablet_presets.dm

@@ -5,6 +5,7 @@
 /obj/item/modular_computer/pda/heads
 	greyscale_config = /datum/greyscale_config/tablet/head
 	greyscale_colors = "#67A364#a92323"
+	max_capacity = parent_type::max_capacity * 2
 	starting_programs = list(
 		/datum/computer_file/program/crew_manifest,
 		/datum/computer_file/program/status,