fix: add runId to seed calculations and use seeded random for treasure loot

Fixes #299: Seed calculation now includes runId component per spec (seed = floor × 12345 + runId)
Fixes #298: Treasure loot now uses seeded random instead of Math.random()

Changes:
- Added runId field to CombatState type
- Generated random runId on spire entry in createEnterSpireMode
- Updated getRoomsForFloor, generateSpireRoomType, generateSpireFloorState, generateTreasureLoot to accept and use runId
- Updated all call sites in combat-descent-actions.ts and combatStore.ts
- Treasure loot item count now uses seeded RNG instead of Math.random()

src/lib/game/stores/combatStore.ts

@@ -47,6 +47,9 @@ export const useCombatStore = create<CombatStore>()(
       currentRoomIndex: 0,
       roomsPerFloor: 1,
 
+      // ─── Spec: Run identity (climbing spec §4.2, §7) ────────────────────
+      runId: 0,
+
       // ─── Spec: Descent tracking state ─────────────────────────────────────
       descentPeak: null,
       roomResetState: {},
@@ -166,8 +169,9 @@ export const useCombatStore = create<CombatStore>()(
         set((s) => {
           if (s.currentFloor <= 1) return s;
           const newFloor = s.currentFloor - 1;
-          const rooms = getRoomsForFloor(newFloor, newFloor * 12345);
-          const newRoom = generateSpireFloorState(newFloor, 0, rooms);
+          const seed = newFloor * 12345 + s.runId;
+          const rooms = getRoomsForFloor(newFloor, seed);
+          const newRoom = generateSpireFloorState(newFloor, 0, rooms, s.runId);
           return {
             currentFloor: newFloor,
             currentRoom: newRoom,
@@ -180,7 +184,8 @@ export const useCombatStore = create<CombatStore>()(
 
       exitSpireMode: () => {
         set((s) => {
-          const rooms = getRoomsForFloor(s.exitFloor, s.exitFloor * 12345);
+          const seed = s.exitFloor * 12345 + s.runId;
+          const rooms = getRoomsForFloor(s.exitFloor, seed);
           return {
           spireMode: false,
           currentAction: 'meditate',
@@ -189,7 +194,7 @@ export const useCombatStore = create<CombatStore>()(
           currentFloor: s.exitFloor,
           floorHP: getFloorMaxHP(s.exitFloor),
           floorMaxHP: getFloorMaxHP(s.exitFloor),
-          currentRoom: generateSpireFloorState(s.exitFloor, 0, rooms),
+          currentRoom: generateSpireFloorState(s.exitFloor, 0, rooms, s.runId),
           castProgress: 0,
           clearedFloors: {},
           clearedRooms: {},
@@ -362,6 +367,7 @@ export const useCombatStore = create<CombatStore>()(
         guardianBarrier: state.guardianBarrier,
         guardianBarrierMax: state.guardianBarrierMax,
         meleeSwordProgress: state.meleeSwordProgress,
+        runId: state.runId,
       }),
     }
   )