physics: send MSG_MOVE_START/STOP_ASCEND and START_DESCEND during flight

When flyingActive_, detect Space/X key transitions and emit proper flight
vertical movement opcodes so the server (and other players) see the
correct ascending/descending animation state:

- MSG_MOVE_START_ASCEND  (Space pressed while flying)  → sets ASCENDING flag
- MSG_MOVE_STOP_ASCEND   (Space released while flying) → clears ASCENDING flag
- MSG_MOVE_START_DESCEND (X pressed while flying)      → clears ASCENDING flag
- MSG_MOVE_STOP_ASCEND   (X released while flying)     → clears vertical state

Track wasAscending_/wasDescending_ member state to detect transitions.
Also clear lingering vertical state when leaving flight mode.

include/rendering/camera_controller.hpp

@@ -256,6 +256,8 @@ private:
     bool wasTurningRight = false;
     bool wasJumping = false;
     bool wasFalling = false;
+    bool wasAscending_ = false;   // Space held while flyingActive_
+    bool wasDescending_ = false;  // X held while flyingActive_
     bool moveForwardActive = false;
     bool moveBackwardActive = false;
     bool strafeLeftActive = false;

src/game/game_handler.cpp

@@ -7329,6 +7329,17 @@ void GameHandler::sendMovement(Opcode opcode) {
         case Opcode::MSG_MOVE_HEARTBEAT:
             // No flag changes — just sends current position
             break;
+        case Opcode::MSG_MOVE_START_ASCEND:
+            movementInfo.flags |= static_cast<uint32_t>(MovementFlags::ASCENDING);
+            break;
+        case Opcode::MSG_MOVE_STOP_ASCEND:
+            // Clears ascending (and descending) — one stop opcode for both directions
+            movementInfo.flags &= ~static_cast<uint32_t>(MovementFlags::ASCENDING);
+            break;
+        case Opcode::MSG_MOVE_START_DESCEND:
+            // Descending: no separate flag; clear ASCENDING so they don't conflict
+            movementInfo.flags &= ~static_cast<uint32_t>(MovementFlags::ASCENDING);
+            break;
         default:
             break;
     }

src/rendering/camera_controller.cpp

@@ -217,6 +217,7 @@ void CameraController::update(float deltaTime) {
     bool shiftDown = !uiWantsKeyboard && (input.isKeyPressed(SDL_SCANCODE_LSHIFT) || input.isKeyPressed(SDL_SCANCODE_RSHIFT));
     bool ctrlDown = !uiWantsKeyboard && (input.isKeyPressed(SDL_SCANCODE_LCTRL) || input.isKeyPressed(SDL_SCANCODE_RCTRL));
     bool nowJump = !uiWantsKeyboard && !sitting && !movementSuppressed && input.isKeyJustPressed(SDL_SCANCODE_SPACE);
+    bool spaceDown = !uiWantsKeyboard && !sitting && !movementSuppressed && input.isKeyPressed(SDL_SCANCODE_SPACE);
 
     // Idle camera: any input resets the timer; timeout triggers a slow orbit pan
     bool anyInput = leftMouseDown || rightMouseDown || keyW || keyS || keyA || keyD || keyQ || keyE || nowJump;
@@ -1795,6 +1796,35 @@ void CameraController::update(float deltaTime) {
         }
     }
 
+    // Flight ascend/descend transitions (Space = ascend, X = descend while mounted+flying)
+    if (movementCallback && !externalFollow_) {
+        const bool nowAscending = flyingActive_ && spaceDown;
+        const bool nowDescending = flyingActive_ && xDown && mounted_;
+
+        if (flyingActive_) {
+            if (nowAscending && !wasAscending_) {
+                movementCallback(static_cast<uint32_t>(game::Opcode::MSG_MOVE_START_ASCEND));
+            } else if (!nowAscending && wasAscending_) {
+                movementCallback(static_cast<uint32_t>(game::Opcode::MSG_MOVE_STOP_ASCEND));
+            }
+            if (nowDescending && !wasDescending_) {
+                movementCallback(static_cast<uint32_t>(game::Opcode::MSG_MOVE_START_DESCEND));
+            } else if (!nowDescending && wasDescending_) {
+                // No separate STOP_DESCEND opcode; STOP_ASCEND ends all vertical movement
+                movementCallback(static_cast<uint32_t>(game::Opcode::MSG_MOVE_STOP_ASCEND));
+            }
+        } else {
+            // Left flight mode: clear any lingering vertical movement states
+            if (wasAscending_) {
+                movementCallback(static_cast<uint32_t>(game::Opcode::MSG_MOVE_STOP_ASCEND));
+            } else if (wasDescending_) {
+                movementCallback(static_cast<uint32_t>(game::Opcode::MSG_MOVE_STOP_ASCEND));
+            }
+        }
+        wasAscending_ = nowAscending;
+        wasDescending_ = nowDescending;
+    }
+
     // Update previous-frame state
     wasSwimming = swimming;
     wasMovingForward = nowForward;