Implement Nature Reality Engine: TreeRenderer, L-system, 3D mesh, wind physics, seasonal changes

[Copilot]

Bootstraps the Nature Reality Engine codebase from scratch, implementing a full procedural tree pipeline with GPU-agnostic renderer interface, wind simulation, and seasonal foliage.

Core engine

• engine/nature/LSystem.h/cpp — String-rewriting L-system with Oak, Pine, Willow presets and custom rule support. Configurable axiom, production rules, segment length, angle, radius taper, and iteration depth.
• engine/nature/Mesh.h — GPU-ready indexed mesh types: Vertex (pos/normal/UV/color), Triangle, BranchSegment, LeafQuad, Mesh.
• engine/renderer/Renderer.h — Abstract IRenderer interface covering full frame lifecycle, mesh upload/update (for wind deformation), camera, lights, and texture streaming. Plug any backend (Vulkan, software rasterizer) via TreeRenderer::attachRenderer(IRenderer*).

TreeRenderer (engine/nature/TreeRenderer.h/cpp)

• generate() — Iterates L-system → 3D turtle interpreter (Rodrigues rotation for all 6 orientation symbols) → tapered cylinder tessellation per branch + leaf quads at tips.
• applyWind(dt) — Per-segment spring-damper oscillator driven by sinusoidal force + gustiness. Only end-ring vertices displaced; stiffness scales with branch radius so twigs flex more than trunk.
• setSeason(season) — Spring / Summer / Autumn / Winter leaf/bark colour tints; Winter sets leaf alpha=0. Color-only vertex update, no topology rebuild.
• grow(dt) — Slowly scales segment length and initial radius, then rebuilds mesh for time-lapse growth.

NRE::TreeRenderer tree;
tree.setSpecies(NRE::TreeSpecies::Oak);
tree.setSeason(NRE::Season::Autumn);
tree.generate();                        // L-system → cylinder mesh + leaves

tree.attachRenderer(&myVulkanRenderer);
while (running) {
    tree.applyWind(dt);
    tree.render();                      // dirty-flag upload + submitMesh
}

Supporting subsystems (interfaces)

• WaterRenderer.h — Gerstner wave surface, wind speed, wave mode.
• VegetationSystem.h — Instanced grass/shrub scatter across terrain patch.
• WeatherSystem.h — Time-of-day sun arc, sky ambient, precipitation type; pushes DirectionalLight into IRenderer.

Build & tests

• CMakeLists.txt — nre_engine static lib + artemis_demo executable + two CTest suites.
• tests/test_lsystem.cpp / tests/test_treerenderer.cpp — 19 unit tests covering rewriting correctness, seasonal alpha, wind displacement, growth, position offset, and custom L-system injection.
• examples/artemis_demo/main.cpp — Standalone demo: ASCII cross-section visualisation per species, seasonal cycle walkthrough, wind frame simulation, and growth steps.

Original prompt

Complete TreeRenderer implementation with L-system algorithm
Add 3D mesh generation from L-system branches
Integrate with Vulkan renderer for photorealistic output
Add wind physics and seasonal changes
Connect to full Nature Reality Engine ecosystem

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