feat: add Lua 5.1 addon system with .toc loader and /run command

Foundation for WoW-compatible addon support:

- Vendor Lua 5.1.5 source as a static library (extern/lua-5.1.5)
- TocParser: parses .toc files (## directives + file lists)
- LuaEngine: Lua 5.1 VM with sandboxed stdlib (no io/os/debug),
  WoW-compatible print() that outputs to chat, GetTime() stub
- AddonManager: scans Data/interface/AddOns/ for .toc files,
  loads .lua files on world entry, skips LoadOnDemand addons
- /run <code> slash command for inline Lua execution
- HelloWorld test addon that prints to chat on load

Integration: AddonManager initialized after asset manager, addons
loaded once on first world entry, reset on logout. XML frame
parsing is deferred to a future step.

extern/lua-5.1.5/etc/Makefile

@@ -0,0 +1,44 @@
+# makefile for Lua etc
+
+TOP= ..
+LIB= $(TOP)/src
+INC= $(TOP)/src
+BIN= $(TOP)/src
+SRC= $(TOP)/src
+TST= $(TOP)/test
+
+CC= gcc
+CFLAGS= -O2 -Wall -I$(INC) $(MYCFLAGS)
+MYCFLAGS= 
+MYLDFLAGS= -Wl,-E
+MYLIBS= -lm
+#MYLIBS= -lm -Wl,-E -ldl -lreadline -lhistory -lncurses
+RM= rm -f
+
+default:
+	@echo 'Please choose a target: min noparser one strict clean'
+
+min:	min.c
+	$(CC) $(CFLAGS) $@.c -L$(LIB) -llua $(MYLIBS)
+	echo 'print"Hello there!"' | ./a.out
+
+noparser: noparser.o
+	$(CC) noparser.o $(SRC)/lua.o -L$(LIB) -llua $(MYLIBS)
+	$(BIN)/luac $(TST)/hello.lua
+	-./a.out luac.out
+	-./a.out -e'a=1'
+
+one:
+	$(CC) $(CFLAGS) all.c $(MYLIBS)
+	./a.out $(TST)/hello.lua
+
+strict:
+	-$(BIN)/lua -e 'print(a);b=2'
+	-$(BIN)/lua -lstrict -e 'print(a)'
+	-$(BIN)/lua -e 'function f() b=2 end f()'
+	-$(BIN)/lua -lstrict -e 'function f() b=2 end f()'
+
+clean:
+	$(RM) a.out core core.* *.o luac.out
+
+.PHONY:	default min noparser one strict clean