feat: full match expressions in bootstrap and selfhost

Lower match to if-else for literals, ranges, enum tags, and wildcards.
Fix bootstrap literal arms that always matched; port real arm AST/parser
and Lcx_LowerMatch to selfhost with last-expression return. Expand
pattern_matching example and add parse/use-after-move/double-mut golden
diagnostics. Selfhost-loop remains binary-identical.

tests/error_golden/use_after_move/expected.err

@@ -0,0 +1,7 @@
+error: type errors in project
+error: use of moved value 'a'
+  --> FILE:10:25
+    |
+ 10 |     let c: own String = a;
+    |                         ^
+   = help: the value was moved; clone it or restructure ownership