Unify registry identifiers and registration model

[armalikhani]

Review and unify how plugin identifiers and registries work across the framework.

Tasks:

• Unify identifier key format across all registries and decide on a consistent format (e.g. origin/source/name, origin/namespace/name, or origin/name).
• Evaluate replacing separate registries with a single generic registry.
• Apply a consistent identity model across all extension types.