Use one name for each thing the UI shows (closes #399)

The database target type is called an archive on its badge, in the add target form's type list and on its edit page, and its settings read "Archive expiry" and "Archive rotation" everywhere, the new webhook page included. The retry field is labelled "Delivery attempts", with its help text and error messages to match, on both target forms and in the target list, where a stored 0 shows as one attempt. The target list's other labels take the same capitalisation. The navbar says "Sign out" and the sign-in page "Sign in", and the README follows. The resubmit notice says "webhook". The stored values (`database`, `max_retries`) and their meaning are unchanged.

Model: opus-5-5

templates/login.html

@@ -1,6 +1,6 @@
 {{template "base" .}}
 
-{{define "title"}}Login - Webhooker{{end}}
+{{define "title"}}Sign in - Webhooker{{end}}
 
 {{define "content"}}
 <div class="min-h-screen flex items-center justify-center py-12 px-4">
@@ -52,7 +52,7 @@
                     >
                 </div>
 
-                <button type="submit" class="btn-primary w-full py-3">Sign In</button>
+                <button type="submit" class="btn-primary w-full py-3">Sign in</button>
             </form>
         </div>
     </div>