feat: add disk I/O stats (read/write throughput bars, hotkey 5, auto-scale)

Add a new disk stats category that reads /proc/diskstats, shows read/write
throughput as colored bars (purple/darker purple like network RX/TX), with
optional utilization % overlay in extended mode. Hotkey 5 cycles: aggregate
(sum all whole-disk devices) → per-device → off. Auto-scale with decay and
optional fixed override via --diskmax / diskmax config key.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/internal/stats/stats.go b/internal/stats/stats.go
index ebb81b3..463268f 100644
--- a/internal/stats/stats.go
+++ b/internal/stats/stats.go
@@ -11,12 +11,21 @@ type NetStamp struct {
 	Stamp float64
 }
 
+// DiskStamp holds disk I/O stats and timestamp for delta calculation.
+type DiskStamp struct {
+	SectorsRead  int64
+	SectorsWrite int64
+	IoTicks      int64
+	Stamp        float64
+}
+
 // HostStats holds the latest stats for one host (read-only snapshot).
 type HostStats struct {
 	LoadAvg1, LoadAvg5, LoadAvg15 string
 	Mem                           map[string]int64
 	Net                           map[string]NetStamp
 	CPU                           map[string]collector.CPULine
+	Disk                          map[string]DiskStamp
 }
 
 // Source is the interface the display uses to read current stats.