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.invariant.test.js

@@ -82,16 +82,16 @@ describe('1-list model: turnOrderIds === participants.map(id), no re-sort', () =
     expect(e.turnOrderIds).toEqual(e.participants.map(x => x.id));
   });
 
-  test('reorder cross-init: allowed, list + rotation reflect new order', () => {
+  test('reorder cross-init: blocked (no-op)', () => {
     let e = enc([p('a',10),p('b',7),p('c',3)]);
     e = apply(e, startEncounter(e)); // [a,b,c]
-    e = apply(e, reorderParticipants(e, 'c', 'a')); // drag c before a
-    expect(e.turnOrderIds).toEqual(['c','a','b']);
-    expect(e.turnOrderIds).toEqual(e.participants.map(x => x.id));
+    const r = reorderParticipants(e, 'c', 'a'); // cross-init
+    expect(r.patch).toBeNull();
+    expect(e.turnOrderIds).toEqual(['a','b','c']); // unchanged
   });
 
-  test('reorder: rotation follows new list order', () => {
-    let e = enc([p('a',10),p('b',7),p('c',3)]);
+  test('reorder same-init: rotation follows new list order', () => {
+    let e = enc([p('a',10),p('b',10),p('c',3)]); // a,b tie
     e = apply(e, startEncounter(e)); // [a,b,c], cur=a
     e = apply(e, reorderParticipants(e, 'b', 'a')); // [b,a,c], cur still a
     const rot = walkRotation(e); // start a, next c (wrap), next b, back a