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/doc/lua.css

@@ -0,0 +1,83 @@
+body {
+	color: #000000 ;
+	background-color: #FFFFFF ;
+	font-family: Helvetica, Arial, sans-serif ;
+	text-align: justify ;
+	margin-right: 30px ;
+	margin-left: 30px ;
+}
+
+h1, h2, h3, h4 {
+	font-family: Verdana, Geneva, sans-serif ;
+	font-weight: normal ;
+	font-style: italic ;
+}
+
+h2 {
+	padding-top: 0.4em ;
+	padding-bottom: 0.4em ;
+	padding-left: 30px ;
+	padding-right: 30px ;
+	margin-left: -30px ;
+	background-color: #E0E0FF ;
+}
+
+h3 {
+	padding-left: 0.5em ;
+	border-left: solid #E0E0FF 1em ;
+}
+
+table h3 {
+	padding-left: 0px ;
+	border-left: none ;
+}
+
+a:link {
+	color: #000080 ;
+	background-color: inherit ;
+	text-decoration: none ;
+}
+
+a:visited {
+	background-color: inherit ;
+	text-decoration: none ;
+}
+
+a:link:hover, a:visited:hover {
+	color: #000080 ;
+	background-color: #E0E0FF ;
+}
+
+a:link:active, a:visited:active {
+	color: #FF0000 ;
+}
+
+hr {
+	border: 0 ;
+	height: 1px ;
+	color: #a0a0a0 ;
+	background-color: #a0a0a0 ;
+}
+
+:target {
+	background-color: #F8F8F8 ;
+	padding: 8px ;
+	border: solid #a0a0a0 2px ;
+}
+
+.footer {
+	color: gray ;
+	font-size: small ;
+}
+
+input[type=text] {
+	border: solid #a0a0a0 2px ;
+	border-radius: 2em ;
+	-moz-border-radius: 2em ;
+	background-image: url('images/search.png') ;
+	background-repeat: no-repeat;
+	background-position: 4px center ;
+	padding-left: 20px ;
+	height: 2em ;
+}
+