feat: let a site render its xhtmlmp/html output as a Mews Profile page

A new mews_profile site setting switches the XHTML-MP 1.2 doctype, the
conformance marker, the viewport tag and the default stylesheet link, and
drops raw HTML passthrough and off-site or data: images that the profile's
permitted-element list cannot vouch for.

text/src/lib.rs

@@ -58,7 +58,8 @@ mod tests {
     /// assertions read as the content itself.
     fn render_with(settings: &PageSettings, width: u16, markdown: &str) -> String {
         let doc = parse::markdown(markdown).unwrap();
-        let ctx = RenderCtx { url: "/x", title: "T", settings, width: Some(width) };
+        let ctx =
+            RenderCtx { url: "/x", title: "T", settings, width: Some(width), mews_hosts: None };
         String::from_utf8(Text.render(&doc, &ctx).unwrap().body).unwrap()
     }
 
@@ -213,7 +214,8 @@ mod tests {
     /// `parse::document`, which needs a file, so the unit tests build them.
     fn render_blocks(settings: &PageSettings, width: u16, blocks: Vec<Block>) -> String {
         let doc = Doc { blocks, first_h1: None };
-        let ctx = RenderCtx { url: "/x", title: "T", settings, width: Some(width) };
+        let ctx =
+            RenderCtx { url: "/x", title: "T", settings, width: Some(width), mews_hosts: None };
         String::from_utf8(Text.render(&doc, &ctx).unwrap().body).unwrap()
     }
 
@@ -267,7 +269,13 @@ mod separation_tests {
     fn render(markdown: &str) -> String {
         let doc = parse::markdown(markdown).unwrap();
         let settings = PageSettings { margin_left: 0, margin_right: 0, ..Default::default() };
-        let ctx = RenderCtx { url: "/x", title: "T", settings: &settings, width: Some(40) };
+        let ctx = RenderCtx {
+            url: "/x",
+            title: "T",
+            settings: &settings,
+            width: Some(40),
+            mews_hosts: None,
+        };
         String::from_utf8(Text.render(&doc, &ctx).unwrap().body).unwrap()
     }
 
@@ -299,7 +307,8 @@ mod optional_feature_tests {
 
     fn render_with(settings: &PageSettings, width: u16, markdown: &str) -> String {
         let doc = parse::markdown(markdown).unwrap();
-        let ctx = RenderCtx { url: "/x", title: "T", settings, width: Some(width) };
+        let ctx =
+            RenderCtx { url: "/x", title: "T", settings, width: Some(width), mews_hosts: None };
         String::from_utf8(Text.render(&doc, &ctx).unwrap().body).unwrap()
     }