refactor: name memory/taxi constants, add camera jitter why-comment

- memory_monitor: extract kOneGB and kFallbackRAM constants from 6
  duplicated 1024*1024*1024 expressions; name kFieldPrefixLen for
  /proc/meminfo "MemAvailable:" offset (was bare 13)
- camera: add why-comment on projection matrix jitter — column 2 holds
  NDC x/y offset for TAA/FSR2 sub-pixel sampling
- movement_handler: name kMaxTaxiNodeId (384) with why-comment —
  WotLK TaxiNodes.dbc has 384 entries, bitmask is 12 × uint32

include/game/movement_handler.hpp

@@ -122,8 +122,11 @@ public:
     };
 
     const std::unordered_map<uint32_t, TaxiNode>& getTaxiNodes() const { return taxiNodes_; }
+    // WotLK 3.3.5a TaxiNodes.dbc has 384 entries; the known-taxi bitmask
+    // is 12 × uint32 = 384 bits. Node IDs outside this range are invalid.
+    static constexpr uint32_t kMaxTaxiNodeId = 384;
     bool isKnownTaxiNode(uint32_t nodeId) const {
-        if (nodeId == 0 || nodeId > 384) return false;
+        if (nodeId == 0 || nodeId > kMaxTaxiNodeId) return false;
         uint32_t idx = nodeId - 1;
         return (knownTaxiMask_[idx / 32] & (1u << (idx % 32))) != 0;
     }

src/core/memory_monitor.cpp

@@ -23,9 +23,10 @@ size_t readMemAvailableBytesFromProc() {
 
     std::string line;
     while (std::getline(meminfo, line)) {
-        // Format: "MemAvailable:  123456789 kB"
+        // /proc/meminfo format: "MemAvailable:  123456789 kB"
+        static constexpr size_t kFieldPrefixLen = 13; // strlen("MemAvailable:")
         if (line.rfind("MemAvailable:", 0) != 0) continue;
-        std::istringstream iss(line.substr(13));
+        std::istringstream iss(line.substr(kFieldPrefixLen));
         size_t kb = 0;
         iss >> kb;
         if (kb > 0) return kb * 1024ull;
@@ -42,13 +43,18 @@ MemoryMonitor& MemoryMonitor::getInstance() {
 }
 
 void MemoryMonitor::initialize() {
+    constexpr size_t kOneGB = 1024ull * 1024 * 1024;
+    // Fallback if OS API unavailable — 16 GB is a safe conservative estimate
+    // that prevents over-aggressive asset caching on unknown hardware.
+    constexpr size_t kFallbackRAM = 16 * kOneGB;
+
 #ifdef _WIN32
     ULONGLONG totalKB = 0;
     if (GetPhysicallyInstalledSystemMemory(&totalKB)) {
         totalRAM_ = static_cast<size_t>(totalKB) * 1024ull;
-        LOG_INFO("System RAM detected: ", totalRAM_ / (1024 * 1024 * 1024), " GB");
+        LOG_INFO("System RAM detected: ", totalRAM_ / kOneGB, " GB");
     } else {
-        totalRAM_ = 16ull * 1024 * 1024 * 1024;
+        totalRAM_ = kFallbackRAM;
         LOG_WARNING("Could not detect system RAM, assuming 16GB");
     }
 #elif defined(__APPLE__)
@@ -56,19 +62,18 @@ void MemoryMonitor::initialize() {
     size_t len = sizeof(physmem);
     if (sysctlbyname("hw.memsize", &physmem, &len, nullptr, 0) == 0) {
         totalRAM_ = static_cast<size_t>(physmem);
-        LOG_INFO("System RAM detected: ", totalRAM_ / (1024 * 1024 * 1024), " GB");
+        LOG_INFO("System RAM detected: ", totalRAM_ / kOneGB, " GB");
     } else {
-        totalRAM_ = 16ull * 1024 * 1024 * 1024;
+        totalRAM_ = kFallbackRAM;
         LOG_WARNING("Could not detect system RAM, assuming 16GB");
     }
 #else
     struct sysinfo info;
     if (sysinfo(&info) == 0) {
         totalRAM_ = static_cast<size_t>(info.totalram) * info.mem_unit;
-        LOG_INFO("System RAM detected: ", totalRAM_ / (1024 * 1024 * 1024), " GB");
+        LOG_INFO("System RAM detected: ", totalRAM_ / kOneGB, " GB");
     } else {
-        // Fallback: assume 16GB
+        totalRAM_ = kFallbackRAM;
-        totalRAM_ = 16ull * 1024 * 1024 * 1024;
         LOG_WARNING("Could not detect system RAM, assuming 16GB");
     }
 #endif

src/rendering/camera.cpp

@@ -48,7 +48,10 @@ glm::vec3 Camera::getUp() const {
 }
 
 void Camera::setJitter(float jx, float jy) {
-    // Remove old jitter, apply new
+    // Sub-pixel jitter for temporal anti-aliasing (TAA / FSR2).
+    // Column 2 of the projection matrix holds the NDC x/y offset — modifying
+    // [2][0] and [2][1] shifts the entire rendered image by a sub-pixel amount
+    // each frame, giving the upscaler different sample positions to reconstruct.
     projectionMatrix[2][0] -= jitterOffset.x;
     projectionMatrix[2][1] -= jitterOffset.y;
     jitterOffset = glm::vec2(jx, jy);