Slice Combat Depth (MC-2): enemy-variety server spine — Spitter, Swarmer, 4-type mix (DR-041)

Adds the server-authoritative mechanics for three new enemy archetypes on top of
the Grunt/Charger base, plus the weighted wave-composition that introduces them:

- Spitter: a ranged Husk variant (SpitterState) that holds a preferred range-band
  (advance/retreat/hold via EnemyAIMath.BandVelocity) and fires a telegraphed,
  dodgeable EnemyProjectile. New server EnemyProjectileMoveSystem (integrate +
  store LastStep) + EnemyProjectileDamageSystem (region-filtered swept hit-test
  rebuilt from LastStep — DR-018 anti-tunnelling; players use HitRadius, structures
  a const radius; at-most-once destroy). Concurrent-spit soft cap, soft-fail retry.
- Swarmer: marker tag + deterministic cluster spawn (1 slot = 1 pack;
  EnemyAIMath.ClusterOffset), MaxAlive counts ENTITIES so a pack defers if it
  won't fit.
- 4-type weighted mix: MixBands -> ZoneEnemyMath.WaveSlots/KindForSlot/
  PackSizeForSlot drives both the expedition director and (fork-4a) the base siege,
  with a mandatory MaxAlive cap. Legacy WaveSize/IsChargerSlot kept + parity-tested.
- Discriminator stays component-presence (no enum in Bursted systems): query-
  partition guards keep each enemy moved by exactly one EnemyAISystem pass
  (sole-Position-writer). EnemyTelegraph.IsCharger -> Kind byte for the client cue.

New authoring (Spitter/Swarmer/EnemyProjectile) + expanded director authorings with
tunable mix/cluster defaults. 13 new EditMode tests (mix composition + legacy parity,
band/cluster math, projectile move + cross-region + swept anti-tunnelling regressions);
full suite green before commit.

Dormant until the prefab/subscene wiring lands (next): the new systems guard on
TryGetSingleton/RequireForUpdate, so with no prefabs wired the new types stay inert.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Assets/_Project/Scripts/Authoring/Combat/SwarmerAuthoring.cs

@@ -0,0 +1,25 @@
+using ProjectM.Simulation;
+using Unity.Entities;
+using UnityEngine;
+
+namespace ProjectM.Authoring
+{
+    /// <summary>
+    /// MC-2 — marks a Husk prefab as a SWARMER variant (the "surround" question). Compose WITH
+    /// <see cref="EnemyAuthoring"/> on the prefab root, tuned fast + low-HP + fast frequent low-chip bites (via the
+    /// EnemyAuthoring fields). This bakes only the <see cref="SwarmerTag"/> marker: a Swarmer has NO AI branch (it
+    /// falls through the Grunt seek+strike pass); the tag drives the director's CLUSTER spawn (a pack per slot) + a
+    /// client tint. Keeps EnemyTag + RegionTag like every Husk.
+    /// </summary>
+    public class SwarmerAuthoring : MonoBehaviour
+    {
+        private class SwarmerBaker : Baker<SwarmerAuthoring>
+        {
+            public override void Bake(SwarmerAuthoring authoring)
+            {
+                var entity = GetEntity(authoring, TransformUsageFlags.Dynamic);
+                AddComponent<SwarmerTag>(entity);
+            }
+        }
+    }
+}