Update app READMEs for monorepo

Remove stale submodule references, port numbers, and Running sections.
Add fragment composition details. Create READMEs for federation and account.

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

account/README.md

@@ -0,0 +1,36 @@
+# Account App
+
+User dashboard for the Rose Ash cooperative. Provides account management, newsletter preferences, and widget pages for tickets and bookings.
+
+## Structure
+
+```
+app.py                  # Application factory (create_base_app + blueprints)
+path_setup.py           # Adds project root + app dir to sys.path
+entrypoint.sh           # Container entrypoint (Redis flush, start)
+bp/
+  account/              #   Dashboard, newsletters, widget pages (tickets, bookings)
+  auth/                 #   OAuth client routes + HTTP token exchange for non-coop clients
+  fragments/            #   auth-menu fragment (sign-in button / user menu)
+models/                 # Re-export stubs pointing to shared/models/
+services/               # register_domain_services() — wires all domains
+templates/              # Account-specific templates (override shared/)
+```
+
+## Auth menu
+
+Account serves the `auth-menu` fragment consumed by all other apps' headers. It renders either a sign-in button (anonymous) or the user's email with a dropdown (authenticated), for both desktop and mobile layouts.
+
+## OAuth token exchange
+
+`POST /auth/oauth/token` provides HTTP-based token exchange for non-coop OAuth clients (e.g., Artdag).
+
+## Cross-domain communication
+
+- `services.blog.*` — post queries for page context
+- `services.calendar.*` — calendar/entry queries for bookings panel
+- `services.cart.*` — cart summary + orders for tickets panel
+
+## Fragments served
+
+- **auth-menu** — sign-in button or user email menu (desktop + mobile)