fix: resolve 7 code quality issues across PRs #59-63

- Remove stale kVOffset (-0.15) from zone_highlight_layer hover detection;
  the offset was removed from rendering but left in the hit-test path,
  shifting hover ~15% vertically
- Add null guard for cachedGameHandler_ in ChatPanel::inputTextCallback
  to prevent dereference before first render frame
- Zero WindowBorderSize in world map ImGui window to eliminate gap
  between window edge and map content
- Replace hardcoded cosmic highlight multipliers with displayH×displayH
  square rendering, preserving 1:1 aspect ratio at any resolution
- Skip transport waypoints where serverToCanonical zeroes nonzero input
  instead of silently building paths with broken (0,0,0) coordinates
- Use length-squared check (posLenSq > 1.0) for spline endpoint
  validation instead of per-component != 0 comparison, so entities
  near the world origin are no longer skipped
- Fix off-by-one in ChatPanel::insertChatLink buffer capacity check

src/game/spline_packet.cpp

@@ -299,9 +299,10 @@ bool parseWotlkMoveUpdateSpline(
             packet.setReadPos(prePointCount);
             return false;
         }
-        // Proximity check: if entity position is known, reject endpoints that
-        // are implausibly far from it (catches misinterpreted compressed data).
-        if (entityPos.x != 0.0f || entityPos.y != 0.0f || entityPos.z != 0.0f) {
+        // Proximity check: if entity position is known (not the default 0,0,0
+        // sentinel), reject endpoints that are implausibly far from it.
+        float posLenSq = entityPos.x * entityPos.x + entityPos.y * entityPos.y + entityPos.z * entityPos.z;
+        if (posLenSq > 1.0f) {
             float dx = epX - entityPos.x;
             float dy = epY - entityPos.y;
             float dz = epZ - entityPos.z;