feat: Add template spell picker from spells.yml; polish spell table

- Add yaml-loader; import data/spells.yml at build time
- Add SpellTemplate/SpellsFile types to globals.d.ts
- Add 'Add Template Spell' button that opens a modal picker pre-filling
  all spell fields from the YAML data
- Move spell data files into data/ directory
- Split spell rows into inputs row + full-width notes row (colspan=6)
- Shrink delete column to fit-content; bold spell name input
- Add class column to spell table; change MP cost to free-text input
- Auto-resize spell notes textarea on load and on input
- Add 10px padding between spells for visual separation

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

data/spells.schema.json

@@ -0,0 +1,50 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "data/spells.schema.json",
+  "title": "Spell Sheet",
+  "description": "A collection of Fabula Ultima spells and arcana entries.",
+  "type": "object",
+  "properties": {
+    "spells": {
+      "type": "array",
+      "items": {
+        "type": "object",
+        "properties": {
+          "name": {
+            "type": "string",
+            "description": "Name of the spell or arcana."
+          },
+          "cost": {
+            "type": "string",
+            "minimum": 0,
+            "description": "MP cost to cast the spell."
+          },
+          "targets": {
+            "type": "string",
+            "description": "Who or what the spell affects (e.g. \"One creature\", \"All enemies\")."
+          },
+          "duration": {
+            "type": "string",
+            "description": "How long the spell's effect lasts (e.g. \"Instantaneous\", \"Scene\")."
+          },
+          "description": {
+            "type": "string",
+            "description": "Full effect description and any special rules for the spell."
+          },
+          "class": {
+            "type": "string",
+            "enum": ["arcanist", "chimerist", "elementalist", "entropist", "spiritist"],
+            "description": "The magic-using class this spell belongs to."
+          },
+          "offensive": {
+            "type": "boolean",
+            "description": "Whether the spell is offensive in nature."
+          }
+        },
+        "required": ["name", "cost", "targets", "duration", "description", "class"],
+        "additionalProperties": false
+      }
+    }
+  },
+  "required": ["spells"]
+}