feat: add modular Forth interpreter implementation

Co-authored-by: aider (openrouter/tencent/hy3-preview:free) <aider@aider.chat>

forth_dict.c

@@ -0,0 +1,28 @@
+#include "forth.h"
+
+Word* add_primitive(const char* name, void (*code)(Word*), uint8_t flags) {
+    if (dict_idx >= DICT_SIZE) {
+        printf("Dictionary full\n");
+        return NULL;
+    }
+    Word* w = &dict[dict_idx++];
+    w->prev = dict_head;
+    dict_head = w;
+
+    size_t len = strlen(name);
+    if (len > MAX_NAME_LEN) len = MAX_NAME_LEN;
+    w->flags = flags | (uint8_t)len;
+    strncpy(w->name, name, len);
+    w->name[len] = '\0';
+    w->code = code;
+    w->body = NULL;
+    return w;
+}
+
+Word* lookup_word(const char* name) {
+    for (Word* w = dict_head; w != NULL; w = w->prev) {
+        if (w->flags & (1 << 6)) continue; // Skip hidden words
+        if (strcmp(w->name, name) == 0) return w;
+    }
+    return NULL;
+}