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>

e2e/smoke.spec.ts

@@ -48,7 +48,7 @@ test('full core flow: campaign → character → dice → combat → compendium'
   await page.getByRole('button', { name: 'Add', exact: true }).click();
   await expect(page.getByText('Goblin')).toBeVisible();
   await page.getByRole('button', { name: 'Start combat' }).click();
-  await expect(page.getByText(/Round 1/)).toBeVisible();
+  await expect(page.getByRole('button', { name: 'End' })).toBeVisible(); // combat active
 
   // --- Compendium ---
   await page.getByRole('link', { name: 'Compendium' }).click();