refactor: move error files to api/error/

Step 4.3 of source reorganization - move error-related files:
- DeferredError.zig
- ErrorCode.cpp/h/ts/zig
- ErrorStackFrame.cpp/h
- ErrorStackTrace.cpp/h
- Errorable.zig
- JSErrorCode.zig
- SystemError.zig
- ZigErrorType.zig

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/buntime/api/error/Errorable.zig

@@ -0,0 +1,43 @@
+pub fn Errorable(comptime Type: type) type {
+    return extern struct {
+        result: Result,
+        success: bool,
+
+        pub const Result = extern union {
+            value: Type,
+            err: ZigErrorType,
+        };
+
+        pub fn unwrap(errorable: @This()) !Type {
+            if (errorable.success) {
+                return errorable.result.value;
+            } else {
+                return errorable.result.err.code.toError();
+            }
+        }
+
+        pub fn value(val: Type) @This() {
+            return @This(){ .result = .{ .value = val }, .success = true };
+        }
+
+        pub fn ok(val: Type) @This() {
+            return @This(){ .result = .{ .value = val }, .success = true };
+        }
+
+        pub fn err(code: anyerror, err_value: bun.jsc.JSValue) @This() {
+            return @This(){
+                .result = .{
+                    .err = .{
+                        .code = ErrorCode.from(code),
+                        .value = err_value,
+                    },
+                },
+                .success = false,
+            };
+        }
+    };
+}
+
+const bun = @import("bun");
+const ErrorCode = @import("./ErrorCode.zig").ErrorCode;
+const ZigErrorType = @import("./ZigErrorType.zig").ZigErrorType;