Add project planning docs and repo scaffolding

Vision, requirements, tech stack, and phased roadmap for the space
survival game, plus Unreal-appropriate .gitignore/.gitattributes
and Git LFS setup.

README.md

@@ -0,0 +1,14 @@
+# SpaceGame
+
+A multiplayer space survival game built in Unreal Engine 5: build and maintain a
+ship, explore a galaxy, land on planets, and establish a space station and
+planetary bases as a shared base of operations.
+
+## Docs
+- [Vision](docs/01_VISION.md) — pitch, reference games, scope reality check
+- [Requirements](docs/02_REQUIREMENTS.md) — functional requirements by system (MVP/Core/Stretch)
+- [Tech Stack](docs/03_TECH_STACK.md) — engine, networking, backend, tooling
+- [Roadmap](docs/04_ROADMAP.md) — phased build plan
+
+## Status
+Pre-Phase 0 — planning complete, Unreal project not yet created.