v1.7.5: add healthHeal field — instant HP restore on drug activation

- New healthHeal field: heals current HP immediately on activation, clamped at max
- healthMod unchanged: still modifies derived max HP persistently (wears off with drug)
- _activateDrug: apply healthHeal heal and notify with before/after/max values
- _formatDrugStateSummary: show Heals Xhp for healthHeal, Max Health +X for healthMod
- updateDrugModel: healthHeal added to numericPaths for validation
- KickStart: healthMod 0, healthHeal 2
- KickStart Plus: healthMod 0, healthHeal 3
- KickStart Solo: healthMod 0, healthHeal 2

system.json

@@ -2,7 +2,7 @@
   "id": "zero-engine",
   "title": "Zero Engine (SLA Industries)",
   "description": "A basic game system for SLA Industries using the Zero Engine rules.",
-  "version": "1.7.4",
+  "version": "1.7.5",
   "compatibility": {
     "minimum": 13,
     "verified": "14.359"