Mint branded short links

Requires scope `links:write`. Mints a branded short link for each supplied URL and returns a mapping of original URL to short link. Links are keyed per user, so the same URL shortened twice returns the same link and does not consume additional quota. UTM handling: any utm_* params already on the URL are preserved and win; defaults (`utm_source=social`, `utm_medium=social`, a month-bucketed `utm_campaign`) only fill the ones the caller did not set. A URL that is already a short link, or that resolves to a private network address, is skipped. A URL that fails to mint is omitted from `links` rather than failing the whole request. Note posts created via `POST /posts` already shorten their links automatically — this endpoint is for shortening without posting.

curl -X POST "https://example.com/short_links" \  -H "Content-Type: application/json" \  -d '{    "urls": [      "string"    ]  }'

{  "links": {    "property1": "string",    "property2": "string"  }}