feat(rules): scale spell damage with caster level

DamageEffect gains optional scaling (1dX per N levels, capped) and scaling_flat (+X per N levels, capped) specs; effective_formula resolves them against the caster's level at cast time, so scaled dice flow through crits, energy resistance and metamagic like the base formula (CRB Magic - Caster Level). Loader rejects mismatched die types. Data: Fireball/Lightning Bolt 1d6/lvl max 10d6, Burning Hands 1d4/lvl max 5d4, Shocking Grasp 1d6/lvl max 5d6, Inflict Light Wounds +1/lvl max +5 (SRD-verified). Cure Light Wounds stays flat: its golden transcript pins 1d8+1 and HealEffect scaling is out of scope.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

data/spells/shocking_grasp.json

@@ -9,10 +9,11 @@
   "effects": [
     {
       "type": "damage",
-      "formula": "1d6",
+      "formula": "0",
       "types": ["electricity"],
-      "half_on_save": false
+      "half_on_save": false,
+      "scaling": { "dice": "1d6", "per_levels": 1, "max_dice": 5 }
     }
   ],
-  "description": "Your successful melee touch attack deals 1d6 points of electricity damage per caster level (maximum 5d6) — modeled at caster level 1 (1d6). No save; the +3 attack bonus against metal-armored foes is not modeled."
+  "description": "SRD spells/shocking-grasp.md: your successful melee touch attack deals 1d6 points of electricity damage per caster level (maximum 5d6). No save; the +3 attack bonus against metal-armored foes is not modeled."
 }