Rate-limit KV still silently falls back to HTML_DRAFTS if UPLOAD_RATE_LIMITS unbound

\`getRateLimitStore\` in \`src/index.js\`:

\`\`\`js
function getRateLimitStore(env) {
return env.UPLOAD_RATE_LIMITS ?? env.HTML_DRAFTS;
}
\`\`\`

\`wrangler.toml.example\` now documents the \`UPLOAD_RATE_LIMITS\` binding (fixed in #3), but any deploy from before that change, or anyone who copies an old \`wrangler.toml\`, still silently mixes rate-limit counters into the drafts namespace with no warning — the exact issue #2 originally flagged.

**Ask:** either fail loudly (log a warning, or refuse rate limiting) when \`UPLOAD_RATE_LIMITS\` isn't bound instead of silently reusing \`HTML_DRAFTS\`, or drop the fallback entirely and document it as a required binding.

Start in src/index.js at getRateLimitStore and inspect how the rate-limit path uses the returned KV binding. Check wrangler.toml.example for the documented binding, then choose and implement one of the requested behaviors so an unbound UPLOAD_RATE_LIMITS cannot silently reuse HTML_DRAFTS; verify the resulting configuration or warning behavior.

Written by the indexing model from the issue text.