Default server name is too generic when registry entry name ends in a generic segment

Description

Follow-up to #1877 / #1919 — the namespace prefix stripping now takes the segment after the last / as the default server name. This works well for most cases (io.github.stacklok/fetch → fetch), but some registry entries have generic trailing segments that produce unhelpful default names.

Example: com.paypal/mcp → mcp

The name mcp is valid and duplicate detection would catch collisions, but it's not a useful default — it tells the user nothing about the server.

Options considered

1. Combine org + name (e.g., paypal-mcp): Works for the PayPal case but produces awkward results elsewhere — io.github.stacklok/fetch → stacklok-fetch (implies Stacklok built the server, which usually isn't true), com.postman/postman-mcp-server → postman-postman-mcp-server
2. Replace all / with - (e.g., com.paypal-mcp): What the cloud UI does, but produces long ugly names that get truncated on server cards and some clients complain about long server_name+tool_name strings
3. Heuristic: Only prepend the org segment when the part after / is "too generic" (e.g., mcp, server). Conceptually appealing but defining "generic" is subjective and could be surprising

Priority

Low

Additional Context

This is an edge case — most registry entries have descriptive names after the /. The current behavior is a significant improvement over the pre-#1919 state where every install required manual name editing.

No implementation file, test, or entry point is named. Start by reviewing the namespace-prefix behavior from #1877 and #1919, then determine which generic-segment rule is intended. Done means the chosen behavior is agreed and the PayPal example no longer receives an unhelpful default name without regressing the descriptive examples.