docs: CHANGELOG, README editor section, fix dbc_to_csv build

- CHANGELOG: add World Editor section (12.5k+ lines, 6 modes, 30+ tools)
  and Novel Open Formats section (6/6 replacements, 309 test assertions)
- README: add World Editor section with build/run/CLI examples, format
  summary, and reference to FORMAT_SPEC.md
- Fix dbc_to_csv build: add extern/ to include path for nlohmann/json
  (broke when dbc_loader.cpp gained JSON DBC loading support)

README.md

@@ -29,6 +29,28 @@ Protocol Compatible with **Vanilla (Classic) 1.12 + TBC 2.4.3 + WotLK 3.3.5a**.
 - **Container builds**: Multi-platform Docker build system for Linux, macOS (arm64/x86_64 via osxcross), and Windows (LLVM-MinGW) cross-compilation.
 - **Release**: v1.8.9-preview — 530+ WoW API functions, 140+ events, 664 opcode handlers.
 
+## World Editor
+
+Standalone tool for creating custom WoW zones with novel open format exports.
+
+```bash
+# Build
+cmake --build build --target wowee_editor
+
+# Run
+./build/bin/wowee_editor --data Data
+
+# Batch convert assets
+./build/bin/wowee_editor --convert-m2 Creature/Bear/Bear.m2 --data Data
+./build/bin/wowee_editor --convert-wmo World/WMO/Stormwind/Stormwind.wmo --data Data
+```
+
+**6 editing modes** (Sculpt, Paint, Objects, Water, NPCs, Quests) with 30+ terrain tools, multi-select, time-of-day lighting, quest chains, and full undo/redo.
+
+**6 novel open format replacements** for all Blizzard proprietary formats: WOT/WHM (terrain), WOM (models), WOB (buildings), zone.json (map def), PNG (textures), JSON (data tables). See `tools/editor/FORMAT_SPEC.md` for full specifications.
+
+Exported zones auto-load in the wowee client from `custom_zones/` or `output/` directories.
+
 ## Features
 
 ### Rendering Engine