Show known systems that don’t publish GBFS with informative message

[emmambd]

Description:
Some well-known systems (e.g., “Santander Cycles - London”) don’t publish GBFS feeds and are therefore not listed in results, leaving users unaware of their existence.

Expected behavior:
Display an informative placeholder result for known systems with no public GBFS feed:

"We are aware of the ‘Santander Cycles - London’ system, but it does not publish a public GBFS to our knowledge. If you know of a feed missing from the Mobility Database, add it here!"