Phase 3: combat depth

- Condition durations + auto-expiry: timed conditions tick down on the affected
  combatant's turn and drop at 0 (engine tickConditions; UI rounds field + (Nr) chip)
- Initiative: Roll-all (d20 + per-combatant bonus, re-sort anchored) + group/quantity add
- Combat log: per-round event feed (turns, round changes, damage/heal, expiries,
  removals) + in-memory Undo of the last change
- Encounter difficulty budget: 5e XP thresholds + PF2e level budget (pure lib +
  tests); live difficulty/XP-award readout from monster combatants vs the party
- Combatants carry initBonus + cr/level; compendium add-to-combat passes them

18 new unit tests (durations, applyInitiatives, budget), new combat-depth e2e.

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

src/lib/combat/engine.test.ts

@@ -4,6 +4,7 @@ import {
   addCombatant,
   applyDamage,
   applyHealing,
+  applyInitiatives,
   currentCombatant,
   endEncounter,
   moveCombatant,
@@ -12,6 +13,7 @@ import {
   removeCombatant,
   setTempHp,
   startEncounter,
+  tickConditions,
   updateCombatant,
 } from './engine';
 
@@ -21,6 +23,7 @@ function mk(id: string, initiative: number, hp = 10): Combatant {
     name: id,
     kind: 'monster',
     initiative,
+    initBonus: 0,
     ac: 12,
     hp: { current: hp, max: hp, temp: 0 },
     conditions: [],
@@ -31,7 +34,7 @@ function mk(id: string, initiative: number, hp = 10): Combatant {
 function encounter(combatants: Combatant[]): Encounter {
   return {
     id: 'e1', campaignId: 'c1', name: 'Test', status: 'planning',
-    round: 0, turnIndex: 0, combatants,
+    round: 0, turnIndex: 0, combatants, log: [],
     createdAt: '', updatedAt: '',
   };
 }
@@ -148,3 +151,30 @@ describe('endEncounter', () => {
     expect(endEncounter(encounter([])).status).toBe('ended');
   });
 });
+
+describe('condition durations', () => {
+  it('ticks duration down and removes expired conditions', () => {
+    const c = { ...mk('a', 0), conditions: [{ name: 'Frightened', value: 2, duration: 1 }, { name: 'Prone' }] };
+    const { combatant, expired } = tickConditions(c);
+    expect(expired).toEqual(['Frightened']);
+    expect(combatant.conditions.map((x) => x.name)).toEqual(['Prone']); // indefinite stays
+  });
+
+  it('nextTurn ticks the newly-active combatant and logs expiry', () => {
+    let e = startEncounter(encounter([mk('a', 20), mk('b', 10)]));
+    e = updateCombatant(e, 'b', { conditions: [{ name: 'Dazed', duration: 1 }] });
+    e = nextTurn(e); // b's turn begins -> Dazed expires
+    expect(currentCombatant(e)?.conditions).toHaveLength(0);
+    expect(e.log.some((l) => /Dazed wore off/.test(l.text))).toBe(true);
+  });
+});
+
+describe('applyInitiatives', () => {
+  it('reassigns initiative, re-sorts, and keeps the current combatant anchored', () => {
+    let e = startEncounter(encounter([mk('a', 20), mk('b', 10), mk('c', 5)]));
+    e = nextTurn(e); // current = b
+    e = applyInitiatives(e, { a: 1, b: 2, c: 30 });
+    expect(e.combatants.map((x) => x.id)).toEqual(['c', 'b', 'a']);
+    expect(currentCombatant(e)?.id).toBe('b');
+  });
+});