Smooth Stand→Hold animation transition with 100ms blend

- Set Hold blendTime=100ms in all 5 M2 files (was 0ms, causing jarring snap)
- Play Hold 100ms before Stand ends (3900ms) for overlap blend
- Set Stand.nextAnim=1, Hold.nextAnim=1 in M2 data for engine chaining
- Revert Hold duration from 300000ms (test residue) back to 4000ms

src/markers/markers.zig

@@ -67,7 +67,7 @@ var marker_entities: [NUM_MARKERS]?*anyopaque = .{null} ** NUM_MARKERS;
 var marker_created_tick: [NUM_MARKERS]u32 = .{0} ** NUM_MARKERS;
 var hold_queued: [NUM_MARKERS]bool = .{false} ** NUM_MARKERS;
 
-const STAND_DURATION_MS: u32 = 4000;
+const STAND_DURATION_MS: u32 = 3900;
 
 // Entities playing their Decay animation before destruction.
 // Cleaned up every frame by luaProcessAnimations (via Lua OnUpdate).