Quests: restart resets variables, respawns giver and NPCs; final failures

Quest audit (docs/quest-audit.md, tools/questscript.mjs), fixes 2-8.
New mods/questscript.cpp scans the script code once (giver, own variables,
needed NPCs, QIS_OnEnter creations, story-ending failure labels).
questfail: generic, giverless, story-ending and NPC-gone failures stay
final; a restart restores the variables snapshot taken at Quest_Trigger,
deletes OnEnter leftovers, respawns the giver and needed NPCs and gives the
accept dialog back. questgiver slimmed on top of questscript.

Not yet tested in game.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CMakeLists.txt

@@ -84,6 +84,7 @@ add_library(sacredK SHARED
     src/mods/questgiver.cpp
     src/mods/questitems.cpp
     src/mods/questnpc.cpp
+    src/mods/questscript.cpp
     src/mods/anticheat.cpp
     src/mods/loadingscreen.cpp
 )