V2 Phase 1: mechanics kernel + compendium→sheet integration

Lay the foundation for full rules enforcement: a new pure, testable
mechanics kernel (src/lib/mechanics/) that derives structured, enforceable
game data from the loosely-typed compendium, plus the first user-facing
payoff (accurate armor AC + spell mechanics on the sheet).

- normalizers: spell (5e + pf2e), armor, monster defenses → typed
  SpellMechanics / ArmorMechanics / DamageDefenses, with memoized derivers
  wrapping the existing lazy compendium loaders (no new assets). 11 unit tests.
- character schema: spell entries snapshot concentration/save/damage at
  compendium-link time; new top-level `concentration` slot and structured
  `equippedArmor` (additive, defaulted). Dexie v14 migration backfills.
- AC model: baseArmorClass now consults equippedArmor (heavy = flat, medium =
  Dex-capped) and falls back to the old 10+Dex formula when unarmored. Threaded
  through every AC call site; armor picker added to the sheet (5e).
- compendium "Add spell to character" snapshots real mechanics via the kernel.

Backward-compatible: un-enriched spells/characters behave exactly as before.
Build + 244 unit tests green; armor→AC verified live in preview.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/features/world/DashboardPage.tsx

@@ -163,7 +163,7 @@ function Dashboard({ campaign }: { campaign: Campaign }) {
 }
 
 function PartyRow({ c, sys }: { c: Character; sys: ReturnType<typeof getSystem> }) {
-  const ac = sys.baseArmorClass({ level: c.level, abilities: c.abilities, armorBonus: c.armorBonus });
+  const ac = sys.baseArmorClass({ level: c.level, abilities: c.abilities, armorBonus: c.armorBonus, ...(c.equippedArmor ? { equippedArmor: c.equippedArmor } : {}) });
   const ratio = c.hp.max > 0 ? c.hp.current / c.hp.max : 0;
   const tone = ratio < 0.35 ? 'var(--app-danger)' : undefined;
   return (