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/Simulation/Combat/MixBands.cs

@@ -0,0 +1,30 @@
+using Unity.Entities;
+
+namespace ProjectM.Simulation
+{
+    /// <summary>
+    /// MC-2 — baked weighted-composition table shared by BOTH enemy directors (the expedition
+    /// ZoneEnemyDirectorSystem and the base-siege WaveSystem). Pure integer weights consumed by the deterministic
+    /// <see cref="ZoneEnemyMath"/>.{WaveSlots, KindForSlot, PackSizeForSlot} functions (no enum, no RNG -&gt;
+    /// replay/save-stable). Per kind: a base count + a per-epoch ramp; the Grunt count is the REMAINDER (slots minus
+    /// the others) so it stays a fixed floor while chargers / spitters / swarmer-slots grow as the epoch (expedition)
+    /// or wave (base siege) climbs. A "swarmer slot" expands to a PackSize cluster at spawn (PackSizeForSlot), so one
+    /// slot = one pack. The LEGACY band {GruntBase=g, ChargerBase=c, ChargerPerEpoch=1, rest 0} reproduces the old
+    /// 2-type <see cref="ZoneEnemyMath.WaveSize"/> / <see cref="ZoneEnemyMath.IsChargerSlot"/> exactly (a parity test
+    /// pins this, so the base-siege size curve is provably unchanged where it must be).
+    /// </summary>
+    public struct MixBands : IComponentData
+    {
+        public int GruntBase;
+        public int ChargerBase;
+        public int SpitterBase;
+        public int SwarmerSlotBase;
+        public int ChargerPerEpoch;
+        public int SpitterPerEpoch;
+        public int SwarmerSlotPerEpoch;
+
+        /// <summary>Exposed-but-default-0 epoch ramp for the swarmer PACK size (PackSizeForSlot adds
+        /// SwarmerPackPerEpoch*(epoch-1) to the director's base pack size). v1 keeps it 0 = fixed pack size.</summary>
+        public int SwarmerPackPerEpoch;
+    }
+}