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>

README.md

@@ -1,17 +1,52 @@
 # vitals
 
-Viewer for the CSV logs written by `vitals-log` (`~/.local/bin/vitals-log`, run
-every minute by the `vitals-log.timer` systemd user unit). Shows the latest
-reading and time-series plots of temperatures, battery, memory, memory pressure
-and load. Built with egui and egui_plot.
+Logs system temperatures, power status and memory load once a minute, and plots
+the history.
+
+- `vitals-log` takes one sample and appends it to `vitals-YYYY-MM.csv`. A
+  systemd user timer runs it every minute.
+- `vitals` is the viewer: the latest reading plus time-series plots, built with
+  egui and egui_plot.
+
+## Install
+
+    make install
+
+This builds both binaries into `~/.local/bin`, installs and starts
+`vitals-log.timer` (systemd user unit), and installs the `Vitals` desktop entry
+so the viewer shows up in the launcher. `PREFIX=/somewhere make install` changes
+where the binaries go; the unit and desktop entry are generated from the
+templates in `dist/` to point at them. The pieces can be installed separately
+with `make install-bin`, `install-units` and `install-desktop`.
+
+`make uninstall` removes all of it and leaves the logs alone. For logging to
+continue while logged out, enable lingering once: `loginctl enable-linger`.
+
+## Logger
+
+    vitals-log [--dir PATH] [--print]
+
+Logs go to `$XDG_STATE_HOME/vitals` (`~/.local/state/vitals`), one file per
+month, about 5 MB each. `--print` writes the header and a sample to stdout
+without touching the log, which is the quick way to check what a machine
+exposes.
+
+The columns are fixed and defined in `src/sample.rs`: temperatures come from
+hwmon chips looked up by name (the `hwmonN` numbering changes between boots),
+power from `/sys/class/power_supply` and `powerprofilesctl`, memory from
+`/proc/meminfo` and `/proc/pressure/memory`. The sensor table is specific to
+this laptop (Framework, Intel); on other hardware, edit `TEMPERATURES`. A source
+that can't be read leaves an empty cell. If the column set changes mid-month,
+the old file is renamed `vitals-YYYY-MM.until-<timestamp>.csv` so layouts never
+mix in one file.
+
+## Viewer
 
-    cargo install --path .
     vitals [--dir PATH] [--interval SECONDS] [--range 1h|6h|24h|7d|all]
 
-The log directory defaults to `$XDG_STATE_HOME/vitals` (`~/.local/state/vitals`).
-Every `vitals-YYYY-MM.csv` there is loaded at startup; after that only bytes
-appended since the last check are read (every 10 s by default). Columns are
-matched by header name, so a changed log layout shows gaps rather than breaking.
+Every `vitals-YYYY-MM.csv` is loaded at startup; after that only bytes appended
+since the last check are read (every 10 s by default). Columns are matched by
+header name, so a changed log layout shows gaps rather than breaking.
 
 Drag to pan and ctrl-scroll or pinch to zoom the time axis; all plots move
 together. Picking a range preset returns to following the clock. Lines break
@@ -19,6 +54,11 @@ where the logger was not running, and on-battery periods are shaded in the
 battery plot. Wide ranges are reduced to per-bucket min/max, so spikes stay
 visible.
 
+## Source
+
+- `src/sample.rs` — reading sensors, appending to the log
 - `src/data.rs` — parsed series, windowing, gap splitting, downsampling
 - `src/tail.rs` — incremental file reader, month rollover, replaced-file reload
-- `src/main.rs` — the UI; the `PANELS` table defines the plots
+- `src/bin/vitals-log.rs` — the logger's command line
+- `src/bin/vitals.rs` — the viewer; the `PANELS` table defines the plots
+- `dist/` — systemd unit and desktop entry templates