Replace _merge_provider_route's five-case nested conditional with a flat
provisioned-wins merge: provider routes claim their hosts outright, manifest
routes for unclaimed hosts append unchanged. Token slot assignment moves to a
single _assign_token_slots pass over the merged list.
Add _route_to_yaml_fields as the single authoritative EgressRoute→YAML mapping,
eliminating the risk of EgressRoute and egress_addon_core.Route silently
drifting apart when new fields are added.
egress_manifest_routes is now a pure lifter with no slot assignment.
_merge_provider_route and _find_or_alloc_token_env are removed.
Tests updated: conflict-die case removed, upgrade-bare replaced with
provider-wins semantics, slot-assignment tests moved to TestSlotAssignment.
didericis-claude
10d0872043