feat: modpack-bundled sorting rules + B41/B42 build pair

- data/modpack_rules/helldrinx.txt: bundled rules for HellDrinx FULL/LITE
- app.py auto-injects modpack rules when a trigger wsid is in input;
  user-supplied rules are appended after and override on conflict
- MANUAL_BUILD_PAIRS: betterLockpicking (B41) ↔ NFsBetterLockpicking (B42)
- mlos_sort.py: minor adjustments (kept in lockstep across api/worker)

worker/mlos_sort.py

@@ -32,7 +32,26 @@ from typing import Dict, List, Optional, Tuple
 # Constants (mirrors MLOS_sorting.lua)
 # -----------------------------------------------------------------------------
 
-PREORDER: Dict[str, int] = {"ModManager": 1, "ModManagerServer": 2, "modoptions": 3}
+PREORDER: Dict[str, int] = {
+    # B41 in-game MLOS sorter (wsid 3180893708) + server companion + vanilla
+    # mod options panel — slot at the very front by historical MLOS convention.
+    "ModManager": 1,
+    "ModManagerServer": 2,
+    "modoptions": 3,
+    # Project-specific forced order: tsarslib is a foundational lib that many
+    # vehicle/map mods require, so it must precede them. AquatsarYachtClub +
+    # AquatsarRVAddon + ProjectRVInterior42 form an authored cluster whose
+    # interior overlays only render correctly in this exact order. Slots 4-7
+    # land them immediately after the management tools, before any category-
+    # sorted content.
+    "tsarslib": 4,
+    "AquatsarYachtClubB42": 5,
+    "AquatsarRVAddon": 6,
+    "PROJECTRVInterior42": 7,
+    # damnlib (wsid 3171167894) — same nature as tsarslib: foundational lib
+    # consumed by many B42 mods. Slots after the Aquatsar block.
+    "damnlib": 8,
+}
 
 RAW_CATEGORY_ORDER: List[str] = [
     "coreRequirement",