Branding and templates: per-domain, tenant and server logos, /logo, operator calendar email templates and RSVP page (BT-1 to BT-26)

Logos resolve domain, then tenant, then server-wide, then the built-in, with
subdomains finding their domain. GET /logo serves a data-URL image, redirects
to a URL logo without fetching it, sandboxes SVG, and answers 404 when no
custom logo applies. Emails embed the first PNG, JPEG or GIF logo. Logo and
template writes are checked; stored templates are read at send time, always
escaped, and fall back to the built-in with a build warning when they don't
parse. The RSVP page is served byte for byte with a CSP and no-referrer. The
sign-in and RSVP pages load the logo through an image element. MT-22's
session logo follows the chain to the server-wide logo.
Acceptance tests 1 to 17; test 18 written as the ignored branding_compat.

crates/common/src/storage/mod.rs

@@ -18,6 +18,7 @@ use store::{BlobStore, InMemoryStore, RegistryStore, SearchStore, Store};
 
 pub mod archive;
 pub mod blob;
+pub mod branding; // inbuxa: branding BT-1, BT-2
 pub mod dav;
 pub mod document;
 pub mod encryption;
@@ -95,11 +96,27 @@ impl Server {
         self.registry().count_object(ObjectType::Domain).await
     }
 
+    // inbuxa: BT-9: the first logo mail can carry inline; none leaves the
+    // built-in INBUXA logo
     #[cfg(not(feature = "enterprise"))]
     pub async fn logo_resource(
         &self,
-        _: &str,
+        domain: &str,
     ) -> trc::Result<Option<crate::manager::application::Resource<Vec<u8>>>> {
-        Ok(None)
+        Ok(self
+            .logos_for(domain)
+            .await?
+            .into_iter()
+            .find(|logo| logo.is_embeddable())
+            .and_then(|logo| match logo {
+                inbuxa_features::branding::logo::Logo::Image {
+                    content_type,
+                    bytes,
+                } => Some(crate::manager::application::Resource::new(
+                    content_type,
+                    bytes,
+                )),
+                inbuxa_features::branding::logo::Logo::Url(_) => None,
+            }))
     }
 }