fix(telnetd): use ext2 path to load clean binary

Update init_shell's program registry to use /sbin/telnetd (ext2 path)
instead of bare "telnetd" which fell back to stale test disk binary
containing debug output.

Also regenerated ext2.img with latest telnetd (no debug output).

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: ryanbreen

testdata/ext2.img

@@ -579,7 +579,7 @@ static PROGRAM_REGISTRY: &[ProgramEntry] = &[
     },
     ProgramEntry {
         name: "telnetd",
-        binary_name: b"telnetd\0",
+        binary_name: b"/sbin/telnetd\0",
         description: "Telnet server on port 2323",
     },
     // === PTY Test ===