Unify top bar button treatment

The patch page already sets the pattern: one filled primary action and
naked buttons for everything else. The issue page and the repo header
used the grey ghost fill instead, so their secondary actions competed
with the primary one.

src/components/RepoHeader.svelte

@@ -149,6 +149,7 @@
       explorerPath={repo.rid}
       id={repo.rid}
       idLabel="repository"
+      variant="naked"
       {config} />
     <CheckoutRepoButton rid={repo.rid} />
   </div>

src/views/repo/Issue.svelte

@@ -396,10 +396,11 @@
           explorerPath={`${repo.rid}/issues/${issue.id}`}
           id={issue.id}
           idLabel="issue"
+          variant="naked"
           {config} />
         <Button
           styleHeight="2rem"
-          variant="ghost"
+          variant="naked"
           onclick={() =>
             show({
               component: CreateIssueModal,