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.

docs/04_ROADMAP.md

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+# Roadmap
+
+Phased so there's a playable build at the end of every phase. Each phase is a
+"piece" in the sense you described — build it, play it, then move to the next.
+Reassess ambition at each phase boundary (see 01_VISION.md).
+
+## Phase 0 — Foundations
+- Install Unreal Engine 5, create the C++ project, set up Git LFS + `.gitignore`.
+- Learn-by-building: a basic pawn that flies in open space with simple physics
+  (no building, no planets yet).
+- Empty test level, no gameplay systems yet.
+- **Exit criteria:** you can fly a placeholder ship around an empty level.
+
+## Phase 1 — Core Ship Loop (single-player)
+- One hand-built ship with hull, power source, thrusters, storage (02_REQUIREMENTS §1 MVP).
+- Basic damage/repair on hull.
+- One hand-authored landable zone (planet or asteroid) with on-foot movement and
+  suit oxygen (02_REQUIREMENTS §4/§6 MVP).
+- Basic resource gathering that feeds a simple inventory.
+- **Exit criteria:** fly from a starting point, land, gather something, fly back.
+
+## Phase 2 — Construction System
+- Modular grid-based building for the ship (attach/detach blocks) (§1 Core).
+- Power/thrust/life-support modeled as real systems blocks contribute to.
+- **Exit criteria:** you can meaningfully redesign your ship, not just pilot a
+  fixed one.
+
+## Phase 3 — Space Station & Planetary Bases
+- A station hub: dock, restock, respawn (§2 MVP/Core).
+- Same construction system adapted for a station and for planet-anchored bases
+  (§5 Core).
+- **Exit criteria:** you have a home base in space and at least one on a planet.
+
+## Phase 4 — Multiplayer (session-based)
+- Integrate Epic Online Services sessions.
+- Replicate ship piloting, block placement, inventory, damage across clients.
+- One host, invited friends join — no persistent backend yet (§7 Core).
+- **Exit criteria:** you and a friend can fly the same ship and build together
+  in a session.
+
+### Decision point
+By here you'll know a lot more about how much solo/small-team bandwidth you
+have. This is the natural point to decide: stay session-based (simpler, still
+a complete game) or push into persistent-world territory (Phase 5+). Both are
+legitimate outcomes.
+
+## Phase 5 — Galaxy Expansion
+- Star map UI + warp travel between multiple hand-authored systems (§3 Core).
+- More planet variety (biomes, hazards) (§4 Core).
+- Crafting/tech tree progression (§8 Core).
+- **Exit criteria:** the game has a galaxy to explore, not just one system.
+
+## Phase 6 — Persistence & Procedural Galaxy (Stretch)
+- Backend service + PostgreSQL for accounts and ownership.
+- Seed-based procedural system/planet generation, storing only deltas.
+- Server-per-system sharding, on-demand instance orchestration.
+- **Exit criteria:** the world persists without a specific host needing to be
+  online, and the galaxy is effectively unbounded.
+
+## Phase 7 — Scale & Polish (Stretch)
+- Matchmaking, base permissions/anti-grief tooling.
+- Console porting (leaning on the EOS choice made in Phase 4).
+- Economy/trading, additional content.
+
+---
+
+**Next step:** Phase 0. Once Unreal Engine is installed and the project is
+created, we can start on the flight pawn and empty test level.