docs: item sales value + PlayFab/master-server backend map

- SALES_VALUE.md: price model (PriceDto/ItemDto.SellPrice/PriceDataComponent), server-authoritative
- BACKEND_PLAYFAB.md: backend = PlayFab Economy + ws:// master server (per-region);
  observed no-playtest boot behavior, capture findings, OnRegionsLoadFailed dialog path
- WEAPON_DAMAGE.md: cross-link to backend doc

docs/WEAPON_DAMAGE.md

@@ -108,6 +108,10 @@ Findings, all consistent with the capstone analysis above:
   the calc itself), and the rich calc `<GetDamage>d__12` factory (0x4BAC460) has **zero**
   callers. So the damage *computation* is not exercised in client-reachable code.
 
+> **Backend identified:** that server is **Azure PlayFab** (Economy v2). The runtime route to
+> these numbers — and whether a base value is catalog-authored in `DisplayProperties` — is in
+> [BACKEND_PLAYFAB.md](BACKEND_PLAYFAB.md), along with how to pull it without tripping BattlEye.
+
 **Conclusion:** the per-weapon damage numbers are **server-authoritative runtime data**.
 They live as Entitas component `value` floats created/assigned by server-side code through
 fully-generic dispatch (no static class/index/string anchor) and reach the client only via