tests: M4 dead-participant skip RED (4 tests, turn.dead-skip.test.js)

Desired behavior locked:
- dead PC not removed from turnOrderIds
- dead PC turn still comes up (nextTurn visits them)
- dead PC on their turn can deathSave
- dead PC not auto-set isActive=false by applyHpChange

All 4 RED on current code. Root cause: nextTurn filters isActive,
applyHpChange sets isActive=false on death, computeTurnOrderAfterRemoval
drops dead from turnOrderIds.

TODO BUG-3/M4 updated with test refs.

TODO.md

@@ -2,7 +2,7 @@
 
 ## M4 — Initiative skip bug + dead-participant handling
 
-### Dead participants must NOT be skipped in turn order
+### Dead participants must NOT be skipped in turn order (BUG-3 / M4)
 - Current: dead (HP=0) → `isActive=false` → removed from turn order → skipped
 - WRONG. Dead participants still occupy initiative slot.
   - PCs (unconscious): death saves still resolve on their turn
@@ -14,7 +14,12 @@
   (sets isActive=false on death), `computeTurnOrderAfterRemoval`.
 - Characterization tests (`src/tests/Combat.characterization.test.js`) lock CURRENT
   (buggy) behavior — those tests must be UPDATED to desired behavior, not
-  preserved. Red desired-test first, then fix.
+  preserved.
+- RED test locked: `shared/tests/turn.dead-skip.test.js` (4 tests).
+  - dead PC not removed from turnOrderIds
+  - dead PC turn still comes up (nextTurn visits them)
+  - dead PC on their turn can deathSave
+  - dead PC not auto-set isActive=false by applyHpChange
 
 ### JUMP_TURN_TO(participantId) manual turn override
 - DM clicks participant → cursor jumps → that participant's turn now.