Vocab file generation (`vocab.bin`) for the C decoder in Flash-MoE.

It seems this file is also missing. An LLM created it after some analysis, and it worked for me.

```
#!/usr/bin/env python3
"""Export vocab.bin for the C decoder (token_id -> string mapping).

Usage: python export_vocab.py [tokenizer.json] [output.bin]

Binary format (must match load_vocab() in infer.m):
uint32_t num_entries
uint32_t max_id
for each entry (sorted by token_id):
uint16_t byte_len
char[byte_len] (UTF-8 bytes)
"""

import json
import struct
import sys
import os


def find_tokenizer():
"""Search common locations for tokenizer.json."""
candidates = []
if len(sys.argv) > 1:
candidates.append(sys.argv[1])
candidates.extend(
[
"tokenizer.json",
"metal_infer/tokenizer.json",
"../tokenizer.json",
]
)
# HuggingFace cache
hf_base = os.path.expanduser("~/.cache/huggingface/hub")
if os.path.isdir(hf_base):
for root, dirs, files in os.walk(hf_base):
if "tokenizer.json" in files:
candidates.append(os.path.join(root, "tokenizer.json"))
for p in candidates:
if os.path.isfile(p):
return p
return None


def main():
tok_path = find_tokenizer()
out_path = (
sys.argv[-1]
if len(sys.argv) > 1 and not sys.argv[-1].endswith(".json")
else "vocab.bin"
)

if not tok_path:
print("ERROR: tokenizer.json not found. Pass as first argument:")
print(" python export...