Initial federation app — ActivityPub server for Rose-Ash

Phase 0+1 of AP integration. New 5th Quart microservice:

Blueprints:
- wellknown: WebFinger, NodeInfo 2.0, host-meta
- actors: AP actor profiles (JSON-LD + HTML), outbox, inbox, followers
- identity: username selection flow (creates ActorProfile + RSA keypair)
- auth: magic link login/logout (ported from blog, self-contained)

Services:
- Registers SqlFederationService (real impl) for federation domain
- Registers real impls for blog, calendar, market, cart
- All cross-domain via shared service contracts

Templates:
- Actor profiles, username selection, platform home
- Auth login/check-email (ported from blog)

Infrastructure:
- Dockerfile + entrypoint.sh (matches other apps)
- CI/CD via Gitea Actions
- shared/ as git submodule

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

.gitmodules

@@ -0,0 +1,4 @@
+[submodule "shared"]
+	path = shared
+	url = https://git.rose-ash.com/coop/shared.git
+	branch = decoupling