Add governed contact point snapshots

docs/IMPLEMENTATION_PLAN.md

@@ -73,6 +73,11 @@ Tasks:
 - [x] define immutable recipient snapshot DTOs
 - [x] expose source provenance in capability responses
 - [x] expose classical address lists as `addresses.recipient_source` sources
+- [x] expose versioned channel-neutral contact-point resolution for local and
+      stable provider subject references
+- [x] support purpose/address-purpose selection, deterministic fallback,
+      locale, and domestic/international postal rendering
+- [x] add bounded source previews and immutable postal/email snapshots
 - [x] add module presence/capability tests
 - [x] document consumer rules for campaign, mail, scheduling, portal, postbox, and
   reporting
@@ -82,6 +87,8 @@ Exit criteria:
 - [x] campaign can request a recipient source via core-mediated capability
 - [x] mail/scheduling can request autocomplete candidates via core-mediated lookup
 - [x] consumers do not import `govoplan_addresses`
+- [x] postal-only contacts/list entries can be resolved without changing the
+      legacy email recipient-source contract
 
 ## Milestone 4: Campaign Integration