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>

webpack.config.js

@@ -65,6 +65,10 @@ module.exports = (env, argv) => {
             },
           },
         },
+        {
+          test: /\.ya?ml$/,
+          use: "yaml-loader",
+        },
         {
           test: /\.css$/,
           use: [