fix: keep the sudo password out of files written as root (0.2.1)

run_command prepended the sudo password to the caller's stdin. A sudo
that does not prompt left it for the command, and fix_snmp's
'cat > snmpd.conf' wrote it as the configuration's first line before
making the file world-readable.

run_command now refuses stdin to a privileged command while a sudo
password is set. fix_snmp stages the configuration in a mktemp file
without privilege, and root installs it next to the target and renames
it over, so nothing root runs follows a symlink.

Closes #8

CHANGELOG.md

@@ -7,6 +7,17 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [0.2.1] - 2026-10-16
+
+### Fixed
+- A sudo password no longer ends up in `snmpd.conf`. `run_command` sent the
+  password and the data on the same stdin, and a sudo that does not prompt
+  (NOPASSWD, a cached timestamp) left the password for `cat`, which wrote it
+  as the first line of a file then made world-readable (#8). `run_command` now
+  refuses stdin to a privileged command while a sudo password is set, and
+  `fix_snmp` stages the configuration without privilege before root installs
+  it, without following a symlink at the target.
+
 ## [0.2.0] - 2026-10-13
 
 ### Changed