docs: update AGENTS.md and CHANGELOG for common/ rename

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: hawkkiller

AGENTS.md

@@ -5,7 +5,7 @@
 This is a Flutter workspace:
 
 - [app](app) — entry point; features and wiring.
-- [core](core) — reusable, app-independent, pub.dev-publishable; use `common` prefix.
+- [common](common) — reusable, app-independent, pub.dev-publishable; use `common` prefix.
 
 ## Architecture
 

CHANGELOG.md

@@ -14,6 +14,7 @@ Version format: `major.minor`. Major version is incremented for brea
 
 - Update Flutter SDK to 3.41 (stable channel)
 - Move `home` and `settings` feature packages to `app`
+- Rename common packages to have `common` prefix
 
 ## [3.10] - Jan 4, 2025