ipx user rename: give an account the name the proxy signs it in as

An account made by hand before the proxy was set up is called what it was
given ('rays'), while Cloudflare Access vouches for an email address. With
auto_create_users on, the first visit through the tunnel would make a
second, empty account. Renaming keeps the id, so feeds, read state and
admin rights go with it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TAC7sLVqfKmY6rsTLXzNgk

src/main.rs

@@ -99,6 +99,9 @@ enum UserCmd {
     Passwd { name: String },
     /// Delete an account and everything it knows: its subscriptions and read state
     Rm { name: String },
+    /// Rename an account, keeping its feeds, read state and admin rights. This is how an
+    /// account made before the proxy takes the name the proxy signs it in as
+    Rename { name: String, new_name: String },
 }
 
 /// What a brand new database starts with, so there is always a way in. Announced loudly
@@ -297,6 +300,22 @@ fn user_cmd(ctx: &Arc<Ctx>, cmd: UserCmd) -> Result<()> {
             println!("password changed for {name}");
             Ok(())
         }
+        UserCmd::Rename { name, new_name } => {
+            let name = name.trim().to_ascii_lowercase();
+            // The same rules as a name the proxy vouches for, or the proxy would never find it.
+            let new_name = crate::auth::name_from_header(&new_name)
+                .ok_or_else(|| anyhow::anyhow!("not a usable name: no commas, semicolons or line breaks"))?;
+            let user = ctx
+                .db
+                .user_by_name(&name)?
+                .ok_or_else(|| anyhow::anyhow!("no such account: {name}"))?;
+            if ctx.db.user_by_name(&new_name)?.is_some() {
+                anyhow::bail!("{new_name} already exists");
+            }
+            ctx.db.rename_user(user.id, &new_name)?;
+            println!("renamed {name} to {new_name}");
+            Ok(())
+        }
         UserCmd::Rm { name } => {
             let name = name.trim().to_ascii_lowercase();
             let user = ctx