Implement WoW-accurate DBC-driven sky system with lore-faithful celestial bodies

Add SkySystem coordinator that follows WoW's actual architecture where skyboxes
are authoritative and procedural elements serve as fallbacks. Integrate lighting
system across all renderers (terrain, WMO, M2, character) with unified parameters.

Sky System:
- SkySystem coordinator manages skybox, celestial bodies, stars, clouds, lens flare
- Skybox is authoritative (baked stars from M2 models, procedural fallback only)
- skyboxHasStars flag gates procedural star rendering (prevents double-star bug)

Celestial Bodies (Lore-Accurate):
- Two moons: White Lady (30-day cycle, pale white) + Blue Child (27-day cycle, pale blue)
- Deterministic moon phases from server gameTime (not deltaTime toys)
- Sun positioning driven by LightingManager directionalDir (DBC-sourced)
- Camera-locked sky dome (translation ignored, rotation applied)

Lighting Integration:
- Apply LightingManager params to WMO, M2, character renderers
- Unified lighting: directional light, diffuse color, ambient color, fog
- Star occlusion by cloud density (70% weight) and fog density (30% weight)

Documentation:
- Add comprehensive SKY_SYSTEM.md technical guide
- Update MEMORY.md with sky system architecture and anti-patterns
- Update README.md with WoW-accurate descriptions

Critical design decisions:
- NO latitude-based star rotation (Azeroth not modeled as spherical planet)
- NO always-on procedural stars (skybox authority prevents zone identity loss)
- NO universal dual-moon setup (map-specific celestial configurations)

README.md

@@ -9,10 +9,12 @@ A native C++ client for World of Warcraft 3.3.5a (Wrath of the Lich King) with a
 ### Rendering Engine
 - **Terrain** -- Multi-tile streaming with async loading, texture splatting (4 layers), frustum culling
 - **Water** -- Animated surfaces, reflections, refractions, Fresnel effect
-- **Sky** -- Dynamic day/night cycle, sun/moon with orbital movement
-- **Stars** -- 1000+ procedurally placed stars (night-only)
-- **Atmosphere** -- Procedural clouds (FBM noise), lens flare with chromatic aberration
-- **Moon Phases** -- 8 realistic lunar phases with elliptical terminator
+- **Sky System** -- WoW-accurate DBC-driven lighting with skybox authority
+  - **Skybox** -- Camera-locked celestial sphere (M2 model support, gradient fallback)
+  - **Celestial Bodies** -- Sun (lighting-driven), White Lady + Blue Child (Azeroth's two moons)
+  - **Moon Phases** -- Server time-driven deterministic phases (30-day / 27-day cycles)
+  - **Stars** -- Baked into skybox assets (procedural fallback for development/debug only)
+- **Atmosphere** -- Procedural clouds (FBM noise), lens flare with chromatic aberration, cloud/fog star occlusion
 - **Weather** -- Rain and snow particle systems (2000 particles, camera-relative)
 - **Characters** -- Skeletal animation with GPU vertex skinning (256 bones), race-aware textures
 - **Buildings** -- WMO renderer with multi-material batches, frustum culling, 160-unit distance culling
@@ -124,8 +126,8 @@ make -j$(nproc)
 | F1 | Performance HUD |
 | F2 | Wireframe mode |
 | F9 | Toggle time progression |
-| F10 | Toggle sun/moon |
-| F11 | Toggle stars |
+| F10 | Toggle celestial bodies (sun + moons) |
+| F11 | Toggle procedural stars (debug mode) |
 | +/- | Change time of day |
 | C | Toggle clouds |
 | L | Toggle lens flare |
@@ -145,6 +147,7 @@ make -j$(nproc)
 - [Authentication](docs/authentication.md) -- SRP6 auth protocol details
 - [Server Setup](docs/server-setup.md) -- Local server configuration
 - [Single Player](docs/single-player.md) -- Offline mode
+- [Sky System](docs/SKY_SYSTEM.md) -- Celestial bodies, Azeroth astronomy, and WoW-accurate sky rendering
 - [SRP Implementation](docs/srp-implementation.md) -- Cryptographic details
 - [Packet Framing](docs/packet-framing.md) -- Network protocol framing
 - [Realm List](docs/realm-list.md) -- Realm selection system
@@ -158,6 +161,13 @@ make -j$(nproc)
 - **Architecture**: Modular design with clear separation (core, rendering, networking, game logic, asset pipeline, UI, audio)
 - **Networking**: Non-blocking TCP, SRP6a authentication, RC4 encryption, WoW 3.3.5a protocol
 - **Asset Loading**: Async terrain streaming, lazy loading, MPQ archive support
+- **Sky System**: WoW-accurate DBC-driven architecture
+  - **Skybox Authority**: Stars baked into M2 sky dome models (not procedurally generated)
+  - **Lore-Accurate Moons**: White Lady (30-day cycle) + Blue Child (27-day cycle)
+  - **Deterministic Phases**: Computed from server game time (consistent across sessions)
+  - **Camera-Locked**: Sky dome uses rotation-only transform (translation ignored)
+  - **No Latitude Math**: Per-zone artistic constants, not Earth-like planetary simulation
+  - **Zone Identity**: Different skyboxes per continent (Azeroth, Outland, Northrend)
 
 ## License