Add plugin name prefix to user-invoked skills / commands

[zikajk]

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Some agentic tools add plugin prefix before its skills and commands - to avoid collision and simplify discovery.
It looks like /<plugin-name>:<skill|command-name>. I think that makes sense for ECA too.

Following might be nice to have:

1. When the prefix and skill|command share the name, prefix is usually removed. (eg. no /ui-doomer:ui-doomer, just /ui-doomer).
2. And when there is no collision, the command/skill can have both short and prefixed form, but I am not sure it is worth increasing the complexity.