boot_splash/image was still on ranaze-loader-icon-v1.png, the mark
from before the app rebranded to the shield "RZ" logo (c91e70d). Point
it at assets/branding/ranaze-mark.png, the same mark already used for
the in-app header brand throughout the current UI.
project.godot's API URLs already pointed at UAT (us3q.ranaze.com), but
deployment_environment itself was still "development" - a leftover
label that never matched the actual origin. Since the UAT-only feature
gates (Dynamic Questions, CCS Cases, Flashcards) check for the literal
"uat" value, running from the Godot editor/debugger hid all three even
though it's UAT in every other respect.
Set it to "uat" to match reality, and update the two places that
sed-patch this value at build time (web/Dockerfile for the UAT/PRD web
builds, tools/export_steam_release.sh for the Steam build) so they
still match the source string they're replacing.
Replace the default Godot boot splash and exe icon with the RanaZe
mark so a Windows build reads as RanaZe from first launch, not the
engine it's built on.
Adds a full flashcards system: FSRS-based scheduling, cloze/basic
card types, CSV import/export, media storage, and study UI, wired
into navigation and the dashboard alongside existing question flows.