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>

package.json

@@ -25,6 +25,7 @@
     "typescript": "^6.0.3",
     "webpack": "^5.107.2",
     "webpack-cli": "^7.0.3",
-    "webpack-dev-server": "^5.2.4"
+    "webpack-dev-server": "^5.2.4",
+    "yaml-loader": "^0.9.0"
   }
 }