Sign-in/sign-up and RepostCard used the static (light-only) color
tokens instead of useTheme() — in dark mode the login screen kept a
light background with light-theme-colored text baked in, and
RepostCard's text color was hardcoded independent of its (already
theme-aware) surrounding background, both landing on illegible
low-contrast text. Same bug class as earlier dark-mode fixes this
session, converted the same way (useTheme() + makeStyles(colors)).
Also add a root-level .easignore (EAS Build's archive root may resolve
above mobile/ for monorepo purposes) excluding backend/tooling
directories the mobile app never needs at build or runtime (.claude,
.impeccable, .planning, docker, prisma — the last is only a type-only
dependency via mobile's tRPC router import, erased before Metro
bundles anything).