Drop the isManual flag from ElementReference and the discovery-state methods
from RegistryInterface. The Registry becomes a flat last-write-wins map;
DiscoveryLoader owns its own owned-set bookkeeping so re-running discovery
only removes elements it itself contributed. Adds ChainLoader for explicit
composition. Manual-over-discovered precedence is preserved via loader
ordering, not a flag on the reference.
* Remove `getSummary` method and update descriptions in snapshots and code
* Add changelog entry
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Co-authored-by: Christopher Hertel <mail@christopher-hertel.de>
