fix(render): code quality cleanup

Magic number elimination:
- Create protocol_constants.hpp, warden_constants.hpp,
  render_constants.hpp, ui_constants.hpp
- Replace ~55 magic numbers across game_handler, warden_handler,
  m2_renderer_render

Reduce nesting depth:
- Extract 5 parseEffect* methods from handleSpellLogExecute
  (max indent 52 → 16 cols)
- Extract resolveSpellSchool/playSpellCastSound/playSpellImpactSound
  from 3× duplicate audio blocks in handleSpellGo
- Flatten SMSG_INVENTORY_CHANGE_FAILURE with early-return guards
- Extract drawScreenEdgeVignette() for 3 duplicate vignette blocks

DRY extract patterns:
- Replace 12 compound expansion checks with isPreWotlk() across
  movement_handler (9), chat_handler (1), social_handler (1)

const to constexpr:
- Promote 23+ static const arrays/scalars to static constexpr across
  12 source files

Error handling:
- Convert PIN auth from exceptions to std::optional<PinProof>
- Add [[nodiscard]] to 15+ initialize/parse methods
- Wrap ~20 unchecked initialize() calls with LOG_WARNING/LOG_ERROR

Signed-off-by: Pavel Okhlopkov <pavel.okhlopkov@flant.com>

src/network/world_socket.cpp

@@ -110,12 +110,12 @@ namespace wowee {
 namespace network {
 
 // WoW 3.3.5a RC4 encryption keys (hardcoded in client)
-static const uint8_t ENCRYPT_KEY[] = {
+static constexpr uint8_t ENCRYPT_KEY[] = {
     0xC2, 0xB3, 0x72, 0x3C, 0xC6, 0xAE, 0xD9, 0xB5,
     0x34, 0x3C, 0x53, 0xEE, 0x2F, 0x43, 0x67, 0xCE
 };
 
-static const uint8_t DECRYPT_KEY[] = {
+static constexpr uint8_t DECRYPT_KEY[] = {
     0xCC, 0x98, 0xAE, 0x04, 0xE8, 0x97, 0xEA, 0xCA,
     0x12, 0xDD, 0xC0, 0x93, 0x42, 0x91, 0x53, 0x57
 };