Initial import: LibreForts (M0-M5 in progress)

Open-source Forts clone: custom C++20 engine + data-driven (Lua) 2D physics
artillery RTS.

- Building: node/strut graph on a stiff mass-spring solver (canon Forts model),
  triangulation rigidity, axial + 30-degree angle-stress breaking, cascading
  collapse, fire (DoT + spread), ground destroys debris.
- Weapons (M4): cannon (ballistic) + laser (beam/ignite) with select-and-aim-in-
  arc UX; splash / beam damage; bg-brace passthrough.
- Devices + economy (M5): reactors + win/loss + restart, mines/turbines/battery,
  metal deposits, storage caps, per-shot energy cost.
- Data-driven via Lua/sol2 with a layered mod loader; enemy-fort scenario mod.
- Renderer: SDL3 + textures + ImGui dev UI. stb_image + ImGui vendored.
- Assets: CC0 placeholders only; real game art loaded at runtime from the user's
  own install via forts: paths (bring-your-own; nothing copyrighted committed).

See README.md / CLAUDE.md and research/ + requirements/ for detail.

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+# Build
+builddir/
+builddir-*/
+build/
+
+# Dear ImGui writes this at runtime (window layout)
+imgui.ini
+
+# Personal / bring-your-own-game-asset override mods (see CLAUDE.md section 5).
+# These reference the user's own Forts install and must never be committed.
+data/mods/local-*/
+
+# Dependencies
+subprojects/bgfx*/
+subprojects/box2d-*/
+subprojects/entt-*/
+subprojects/glm-*/
+subprojects/imgui-*/
+subprojects/sol2-*/
+subprojects/soloud-*/
+subprojects/enet/
+
+# IDE
+.idea/
+.vscode/
+*.swp
+*.swo
+*~
+
+# Object files
+*.o
+*.obj
+
+# macOS
+.DS_Store
+
+# Core dumps
+core
+core.*