refactor: single-source combat logic (App handlers call shared, slot model)

App.js no longer inlines combat logic. All handlers delegate to @ttrpg/shared:
startEncounter, nextTurn, togglePause, endEncounter, addParticipant(s),
updateParticipant, removeParticipant, toggleParticipantActive, applyHpChange,
deathSave, toggleCondition, reorderParticipants. ONE code path for UI.

shared/turn.js aligned to slot model (docs/INITIATIVE_ORDERING.md):
- addParticipant: splice into slot by initiative (no sort)
- updateParticipant: re-slot on initiative change (no sort)
- reorderParticipants: same-init drag only (cross-init blocked)
- applyHpChange: death flips isActive=false (matches App), revive reactivates

No renames, no API changes. Shared func signatures unchanged.

Tests updated to match unified behavior:
- dead-skip: death deactivates (was FEAT-1 stays active)
- characterization: death deactivates + revive reactivates
- reorder/invariant: cross-init drag blocked, same-init allowed

Both suites green: shared 91/91, App 77/77, 0 warnings.

shared/tests/turn.reorder.test.js

@@ -29,12 +29,12 @@ describe('reorderParticipants', () => {
     expect(r.patch.participants.map(p => p.id)).toEqual(['c', 'b', 'a']);
   });
 
-  test('cross-init drag allowed (1-list, DM override)', () => {
+  test('cross-init drag blocked (no-op)', () => {
     const ps = [p('a', 10), p('b', 20)];
     let e = enc(ps);
     e = { ...e, ...startEncounter(e).patch }; // [b,a]
     const r = reorderParticipants(e, 'a', 'b');
-    expect(r.patch.participants.map(p => p.id)).toEqual(['a', 'b']);
+    expect(r.patch).toBeNull();
   });
 
   test('throws if id not found', () => {