Rewrite the logger in Rust; add install targets

vitals-log replaces the bash sampler and writes the same CSV layout.
The crate is now a library plus two binaries. dist/ holds the systemd
unit and desktop entry templates, installed by make install.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

dist/vitals.desktop

@@ -0,0 +1,10 @@
+[Desktop Entry]
+Type=Application
+Name=Vitals
+GenericName=System Vitals History
+Comment=Temperature, power and memory history
+Exec=@BINDIR@/vitals
+Icon=utilities-system-monitor
+Terminal=false
+Categories=System;Monitor;
+StartupWMClass=vitals