feat: flat spell frontmatter, full source-book titles, drop circle

Parser reads human-friendly flat keys (range, targets, castingTime, overcast
list, threshold/successes, ...) and expands them to SpellData; fixes
[object Object] range, empty targets/casting time and blank overcast rows.
SOURCE_BOOKS ids now match vault slugs and show full book titles.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/data/item-spell.ts

@@ -23,7 +23,6 @@ export class SpellData extends foundry.abstract.TypeDataModel {
     const f = fields();
     return {
       // Identification
-      circle: makeIntField(1, { min: 0, max: 9 }),
       school: makeStringField('', { blank: true, choices: SPELL_SCHOOLS as unknown as readonly string[] }),
       discipline: makeStringField(''),
       deity: makeStringField('', { blank: true, choices: SACRED_DEITIES as unknown as readonly string[] }),