Don't allow spaces in mcp server endpoints

[mdeyell-valid-mind]

Creating an MCP server with a space in its name (for example "Slack Local") produces an endpoint that clients cannot reach.

To fix this, I added a slug that can be used to select servers. Now when making a mcp server named slack local, it gets an internal slug of slack-local. The db enforces unique slugs.
I also disallow names that consist entirely of dots .

• endpoint_slug storage on mcp_servers, with a migration that backfills existing servers and handles slug collisions deterministically.
  • Resolver support for looking up servers by endpoint slug as well as by original name.
  • Admin API fields for endpoint_slug and endpoint_url.
  • UI display of the resolved MCP endpoint after create/save and in the server detail panel.
  • Tests covering slug generation, duplicate slug rejection, migration backfill, resolver lookup, and admin API endpoint display.

#115