release: 1.2.0

Close CHANGELOG [Unreleased] as 1.2.0; correct missing entries; bump the
compose pin and image references.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Co-authored-by: Cursor <cursoragent@cursor.com>

docs/plans/inbound-relay.md

@@ -5,7 +5,7 @@
 the implementation lands (do not fix a major in advance).  
 **Order:** recommended next among agreed 1.x+ items (after `internal/web` split
 and the domain-admin role, both shipped — see [CHANGELOG](../CHANGELOG.md)
-`[1.1.0]` and `[Unreleased]`).
+`[1.2.0]`).
 
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