docs: add CONTRIBUTING.md and CHANGELOG.md; optimize chat parser allocation

CONTRIBUTING.md: code style, PR process, architecture pointers, packet
handler pattern, key files for new contributors.

CHANGELOG.md: grouped changes since v1.8.1-preview into Performance,
Bug Fixes, Features, Security, and Code Quality sections.

Chat parser: use stack-allocated std::array<char, 256> for typical chat
messages instead of heap-allocated std::string. Only falls back to heap
for messages > 256 bytes. Reduces allocator pressure on high-frequency
chat packet handling.

CHANGELOG.md

@@ -0,0 +1,53 @@
+# Changelog
+
+## [Unreleased] — changes since v1.8.1-preview (2026-03-23)
+
+### Performance
+- Eliminate ~70 unnecessary sqrt ops per frame; constexpr reciprocals and cache optimizations
+- Skip bone animation for LOD3 models; frustum-cull water surfaces
+- Eliminate per-frame heap allocations in M2 renderer
+- Convert entity/skill/DBC/warden maps to unordered_map; fix 3x contacts scan
+- Eliminate double map lookups and dynamic_cast in render loops
+- Use second GPU queue for parallel texture/buffer uploads
+- Time-budget tile finalization to prevent 1+ second main-loop stalls
+- Add Vulkan pipeline cache persistence for faster startup
+
+### Bug Fixes
+- Fix spline parsing with expansion context; preload DBC caches at world entry
+- Fix NPC/player attack animation to use weapon-appropriate anim ID
+- Fix equipment visibility and follow-target run speed
+- Fix inspect (packed GUID) and client-side auto-walk for follow
+- Fix mail money uint64, other-player cape textures, zone toast dedup, TCP_NODELAY
+- Guard spline point loop against unsigned underflow; guard hexDecode/stoi/stof
+- Fix infinite recursion in toLowerInPlace and operator precedence bugs
+- Fix 3D audio coords for PLAY_OBJECT_SOUND; correct melee swing sound paths
+- Prevent Vulkan sampler exhaustion crash; skip pipeline cache on NVIDIA
+- Skip FSR3 frame gen on non-AMD GPUs to prevent driver crash
+- Fix chest GO interaction (send GAMEOBJ_USE+LOOT together)
+- Restore WMO wall collision threshold; fix off-screen bag positions
+- Guard texture log dedup sets with mutex for thread safety
+- Fix lua_pcall return check in ACTIONBAR_PAGE_CHANGED
+
+### Features
+- Render equipment on other players (helmets, weapons, belts, wrists, shoulders)
+- Target frame right-click context menu
+- Crafting sounds and Create All button
+- Server-synced bag sort
+- Log GPU vendor/name at init
+
+### Security
+- Add path traversal rejection and packet length validation
+
+### Code Quality
+- Packet API: add readPackedGuid, writePackedGuid, writeFloat, getRemainingSize,
+  hasRemaining, hasData, skipAll (replacing 1300+ verbose expressions)
+- GameHandler helpers: isInWorld, isPreWotlk, guidToUnitId, lookupName,
+  getUnitByGuid, fireAddonEvent, withSoundManager
+- Dispatch table: registerHandler, registerSkipHandler, registerWorldHandler,
+  registerErrorHandler (replacing 120+ lambda wrappers)
+- Shared ui_colors.hpp with named constants replacing 200+ inline color literals
+- Promote 50+ static const arrays to constexpr across audio/core/rendering/UI
+- Deduplicate class name/color functions, enchantment cache, item-set DBC keys
+- Extract settings tabs, GameHandler::update() phases, loadWeaponM2 into methods
+- Remove 12 duplicate dispatch registrations and C-style casts
+- Extract toHexString, toLowerInPlace, duration formatting, Lua return helpers