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/double_mut_borrow/bux.toml

@@ -0,0 +1,7 @@
+[Package]
+Name    = "double_mut_borrow"
+Version = "0.1.0"
+Type    = "bin"
+
+[Build]
+Output = "Bin"

tests/error_golden/double_mut_borrow/expected.err

@@ -0,0 +1,6 @@
+error: type errors in project
+error: mutable borrow conflict: arguments 1 and 2 both borrow '&mut x'
+  --> FILE:10:11
+    |
+ 10 |     TwoMut(&x, &x);
+    |           ^

tests/error_golden/double_mut_borrow/src/Main.bux

@@ -0,0 +1,12 @@
+@[Checked]
+func TwoMut(a: &mut int, b: &mut int) {
+    *a = 1;
+    *b = 2;
+}
+
+@[Checked]
+func Main() -> int {
+    var x: int = 0;
+    TwoMut(&x, &x);
+    return 0;
+}

tests/error_golden/parse_error/bux.toml

@@ -0,0 +1,7 @@
+[Package]
+Name    = "parse_error"
+Version = "0.1.0"
+Type    = "bin"
+
+[Build]
+Output = "Bin"

tests/error_golden/parse_error/expected.err

@@ -0,0 +1,7 @@
+error: parse errors in FILE
+error: expected expression
+  --> FILE:2:13
+    |
+ 2 |     let x = ;
+    |             ^
+   = help: the previous statement may be incomplete (missing value or ';')

tests/error_golden/parse_error/src/Main.bux

@@ -0,0 +1,4 @@
+func Main() -> int {
+    let x = ;
+    return 0;
+}

tests/error_golden/run.sh

@@ -16,10 +16,13 @@ passed=0
 failed=0
 
 normalize() {
-  # Replace absolute path prefix with FILE, drop trailing blank lines
+  # Replace absolute paths with FILE (location markers and "in <path>" lines).
+  # Drop trailing blank lines.
   sed -E \
-    -e "s|$DIR/[^:]+:|FILE:|g" \
-    -e "s|$ROOT/[^:]+:|FILE:|g" \
+    -e "s|$DIR/[^:[:space:]]+:|FILE:|g" \
+    -e "s|$ROOT/[^:[:space:]]+:|FILE:|g" \
+    -e "s|$DIR/[^:[:space:]]+|FILE|g" \
+    -e "s|$ROOT/[^:[:space:]]+|FILE|g" \
     -e "s|//+|/|g" \
     | sed -e :a -e '/^\n*$/{$d;N;ba' -e '}'
 }

tests/error_golden/use_after_move/bux.toml

@@ -0,0 +1,7 @@
+[Package]
+Name    = "use_after_move"
+Version = "0.1.0"
+Type    = "bin"
+
+[Build]
+Output = "Bin"

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

tests/error_golden/use_after_move/src/Main.bux

@@ -0,0 +1,12 @@
+@[Checked]
+func Take(s: own String) -> own String {
+    return s;
+}
+
+@[Checked]
+func Main() -> int {
+    let a: own String = "hello";
+    let b: own String = Take(a);
+    let c: own String = a;
+    return 0;
+}