Bug hunt + 5e/PF2e parity + character-build UX overhaul

Audited every calculation (26-agent adversarial workflow + hand-verification).
Core math was sound; fixed real bugs, closed parity gaps, and overhauled the
character-build UX. 396 -> 424 tests; lint clean; build green.

Correctness fixes:
- Heavy armor no longer applies a negative DEX penalty to AC (3 paths + default)
- 5e Exhaustion 4 (HP-max halved) implemented via deriveEffectiveMaxHp + badge
- PF2e dazzled no longer makes a creature easier to hit
- PF2e immunity 'all' zeroes all damage (was misfiled as a condition immunity)
- Director schema bounds; PF2e spell-save basis from the `basic` flag; 5e
  disadvantage-only save guard; remove bogus Concentrating, add Broken/Quickened
- Fix 3 lint errors (useCloud hooks naming, useless escape, explicit any)

PF2e survival subsystem (parity with 5e death saves):
- mechanics/dying.ts (maxDying/isDead/knockOut/applyRecovery/pf2eRestDecay)
- DefensesSection knock-out + recovery-check + death UI; rest-decay in applyRest;
  drained HP reduction

Character-build UX:
- Persisted abilityBuild (base + per-source contributions); sheet & wizard show
  every ability source; higher-level PF2e gains L5/10/15/20 boosts
- Creation surfaces granted skills (incl. new PF2e background skill parsing)
- LevelUpModal enumerates features gained + prompts every owed choice (subclass,
  feats, fighting style, ...) via collectChoices/collectFeatures/subclassPrompt

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/lib/rules/rules.test.ts

@@ -72,6 +72,16 @@ describe('5e derived stats', () => {
     const ac = dnd5e.baseArmorClass(input);
     expect(ac).toBe(10 + 2);
   });
+
+  it('heavy armor (dexCap 0) ignores a negative DEX rather than penalising AC', () => {
+    // regression: Math.min(dexMod, 0) wrongly applied a negative DEX to heavy armor.
+    const lowDex: CharacterRulesInput = {
+      level: 1,
+      abilities: { str: 16, dex: 8, con: 14, int: 10, wis: 12, cha: 8 }, // DEX 8 = -1
+      equippedArmor: { baseAc: 18, dexCap: 0 }, // plate
+    };
+    expect(dnd5e.baseArmorClass(lowDex)).toBe(18); // not 17
+  });
 });
 
 describe('pf2e proficiency', () => {