fix(movement): multi-segment path interpolation, waypoint parsing & terrain Z clamping

Add proper waypoint support to entity movement:

- Parse intermediate waypoints from MonsterMove packets in both WotLK
  and Vanilla paths. Uncompressed paths store absolute float3 waypoints;
  compressed paths decode TrinityCore's packed uint32 deltas (11-bit
  signed x/y, 10-bit signed z, ×0.25 scale, waypoint = midpoint − delta)
  with correct 2's-complement sign extension.

- Entity::startMoveAlongPath() interpolates along cumulative-distance-
  proportional segments instead of a single straight line.

- MovementHandler builds the full path (start → waypoints → destination)
  in canonical coords and dispatches to startMoveAlongPath() when
  waypoints are present.

- Snap entity x/y/z to moveEnd in the dead-reckoning overrun phase
  before starting a new movement, preventing visible teleports when the
  renderer was showing the entity at its destination.

- Clamp creature and player entity Z to the terrain surface via
  TerrainManager::getHeightAt() during active movement. Idle entities
  keep their server-authoritative Z to avoid breaking flight masters,
  elevator riders, etc.

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

src/core/application.cpp

@@ -1756,6 +1756,17 @@ void Application::update(float deltaTime) {
                         inOverrun ? entity->getLatestZ() : entity->getZ());
                     glm::vec3 renderPos = core::coords::canonicalToRender(canonical);
 
+                    // Clamp creature Z to terrain surface during movement interpolation.
+                    // The server sends single-segment moves and expects the client to place
+                    // creatures on the ground.  Only clamp while actively moving — idle
+                    // creatures keep their server-authoritative Z (flight masters, etc.).
+                    if (entity->isActivelyMoving() && renderer->getTerrainManager()) {
+                        auto terrainZ = renderer->getTerrainManager()->getHeightAt(renderPos.x, renderPos.y);
+                        if (terrainZ.has_value()) {
+                            renderPos.z = terrainZ.value();
+                        }
+                    }
+
                     // Visual collision guard: keep hostile melee units from rendering inside the
                     // player's model while attacking. This is client-side only (no server position change).
                     // Only check for creatures within 8 units (melee range) — saves expensive
@@ -1959,6 +1970,14 @@ void Application::update(float deltaTime) {
                         inOverrun ? entity->getLatestZ() : entity->getZ());
                     glm::vec3 renderPos = core::coords::canonicalToRender(canonical);
 
+                    // Clamp other players' Z to terrain surface during movement
+                    if (entity->isActivelyMoving() && renderer->getTerrainManager()) {
+                        auto terrainZ = renderer->getTerrainManager()->getHeightAt(renderPos.x, renderPos.y);
+                        if (terrainZ.has_value()) {
+                            renderPos.z = terrainZ.value();
+                        }
+                    }
+
                     auto posIt = _pCreatureRenderPosCache.find(guid);
                     if (posIt == _pCreatureRenderPosCache.end()) {
                         charRenderer->setInstancePosition(instanceId, renderPos);