feat(repl): implement native Zig REPL for bun repl

This implements a new REPL in Zig that replaces the previous bunx-based
REPL. The new REPL provides:

- Interactive line editing with cursor movement and history navigation
- Syntax highlighting using QuickAndDirtyJavaScriptSyntaxHighlighter
- Multi-line input with bracket matching detection
- REPL commands (.help, .exit, .clear, .load, .save, .editor, .timing)
- JavaScript evaluation using the global eval() function
- Pretty-printed output for evaluated expressions
- Support for both TTY (interactive) and non-TTY (piped) input

The REPL properly initializes the JSC VirtualMachine with the API lock
held, enabling safe JavaScript execution. It uses Bun's transpiler
infrastructure and output formatting.

TODO:
- Implement REPL transforms for variable persistence across lines
- Integrate package installation
- Add shell mode integration
- Implement JSC-based autocomplete

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/cli.zig

@@ -92,6 +92,7 @@ pub const AuditCommand = @import("./cli/audit_command.zig").AuditCommand;
 pub const InitCommand = @import("./cli/init_command.zig").InitCommand;
 pub const WhyCommand = @import("./cli/why_command.zig").WhyCommand;
 pub const FuzzilliCommand = @import("./cli/fuzzilli_command.zig").FuzzilliCommand;
+pub const ReplCommand = @import("./cli/repl_command.zig");
 
 pub const Arguments = @import("./cli/Arguments.zig");
 
@@ -826,12 +827,8 @@ pub const Command = struct {
                 return;
             },
             .ReplCommand => {
-                // TODO: Put this in native code.
-                var ctx = try Command.init(allocator, log, .BunxCommand);
-                ctx.debug.run_in_bun = true; // force the same version of bun used. fixes bun-debug for example
-                var args = bun.argv[0..];
-                args[1] = "bun-repl";
-                try BunxCommand.exec(ctx, args);
+                const ctx = try Command.init(allocator, log, .ReplCommand);
+                try ReplCommand.exec(ctx);
                 return;
             },
             .RemoveCommand => {