Implement D&D 5e death-save state machine and cleanup combat ordering

- Add status-driven death-save model:
  - status: conscious | dying | stable | dead
  - deathSaveSuccesses/deathSaveFailures as display counters
  - remove old death-save fields as source of truth
- Add death-save actions:
  - success, fail, nat1, nat20
  - stabilize participant
  - revive dead participant to 0 HP, stable, unconscious
- Apply 5e HP transition rules:
  - characters and NPCs at 0 HP become dying
  - stable/dying participants gain unconscious condition
  - healing clears death saves and returns conscious
  - massive damage kills
  - non-NPC monsters at 0 HP become dead and inactive
- Split NPCs from monsters with type="npc":
  - NPCs use death saves like characters
  - NPCs remain DM-controlled/monster-colored in UI
  - new NPCs no longer persist isNpc flag
- Keep dead PCs/NPCs in encounter and initiative until DM removes or deactivates
- Allow DM active/inactive toggle for dead participants
- Hide inactive participants from player display
- Improve DM and player death-state UI:
  - show Dying/Dead/Unconscious states consistently
  - add revive button for dead participants
  - distinguish dead visual from inactive visual in DM view
- Fix initiative drag/reorder behavior:
  - downward drag now changes order instead of no-op
  - paused combat can reorder across current turn pointer
  - turnOrderIds stay synced to participants order
- Persist campaign collapse state in localStorage
- Update death-save docs and encounter builder docs
- Add/expand tests for:
  - death saves and HP transitions
  - dead/active/inactive behavior
  - NPC death-save behavior
  - player display visibility
  - drag reorder semantics
  - logging expectations

Tests:
- npm run test:all
- app: 94 passed
- shared: 158 passed, 5 skipped
- server: 32 passed

shared/tests/turn.skip.test.js

@@ -33,7 +33,7 @@ function setup(ctx) {
     buildMonsterParticipant({ name: 'Goblin2', maxHp: 100, initMod: 2 }).participant,
     buildMonsterParticipant({ name: 'OrcBoss', maxHp: 500, initMod: 1 }).participant,
     buildMonsterParticipant({ name: 'Wolf', maxHp: 120, initMod: 3 }).participant,
-    buildMonsterParticipant({ name: 'Merchant', maxHp: 150, initMod: 0, isNpc: true }).participant,
+    buildMonsterParticipant({ name: 'Merchant', maxHp: 150, initMod: 0, asNpc: true }).participant,
   ];
   let e = {
     name: 't', participants: ps, isStarted: false, isPaused: false,