fix: add Char pattern matching and Char comparison operators

- Parser: support Char literals in match patterns (e.g., 'x' => ...)
- Interpreter: add Char comparison for <, <=, >, >= operators
  Previously only Int, Float, and String supported ordering comparisons.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/parser.rs

@@ -1887,6 +1887,14 @@ impl Parser {
                     span: token.span,
                 }))
             }
+            TokenKind::Char(c) => {
+                let c = *c;
+                self.advance();
+                Ok(Pattern::Literal(Literal {
+                    kind: LiteralKind::Char(c),
+                    span: token.span,
+                }))
+            }
             TokenKind::Ident(name) => {
                 // Check if it starts with uppercase (constructor) or lowercase (variable)
                 if name.chars().next().map_or(false, |c| c.is_uppercase()) {