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/auth/auth_handler.cpp

@@ -265,16 +265,15 @@ void AuthHandler::sendLogonProof() {
     const std::array<uint8_t, 20>* crcHashPtr = nullptr;
 
     if (securityFlags_ & kSecurityFlagPin) {
-        try {
-            PinProof proof = computePinProof(pendingSecurityCode_, pinGridSeed_, pinServerSalt_);
-            pinClientSalt = proof.clientSalt;
-            pinHash = proof.hash;
-            pinClientSaltPtr = &pinClientSalt;
-            pinHashPtr = &pinHash;
-        } catch (const std::exception& e) {
-            fail(std::string("PIN required but invalid: ") + e.what());
+        auto proof = computePinProof(pendingSecurityCode_, pinGridSeed_, pinServerSalt_);
+        if (!proof) {
+            fail("PIN required but invalid input");
             return;
         }
+        pinClientSalt = proof->clientSalt;
+        pinHash = proof->hash;
+        pinClientSaltPtr = &pinClientSalt;
+        pinHashPtr = &pinHash;
     }
 
     // Legacy client integrity hash (aka "CRC hash"). Some servers enforce this for classic builds.