Progress pane: ramp/hold countdown with green digits; header ramp+hold rows

Step plates now show "Ramp h:mm:ss" (ramp time only) during ramp phase
and "Hold h:mm:ss" (hold remaining) during hold phase, both in the same
digit area in green (#4ade80). Inactive steps show planned ramp duration.

Header countdown gains a "hold" row alongside the existing "ramp" (renamed
from "step") and "total" rows. All three use the same h:mm:ss format.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SH2D4LRuCnhLSzoYerAfJX

web/style.css

@@ -106,13 +106,15 @@ header#connection-bar {
     width: 2.8em;
 }
 #hdr-step-remaining,
-#hdr-total-remaining {
+#hdr-total-remaining,
+#hdr-hold-remaining {
     font-family: 'Courier New', 'Lucida Console', monospace;
     font-weight: bold;
     font-size: 1.35em;
     color: var(--accent);
 }
 
+
 /* --- Transport buttons (circular, coloured) --- */
 
 .transport-btn {
@@ -327,7 +329,7 @@ header#connection-bar {
     font-weight: bold;
     text-align: right;
     font-family: 'Courier New', monospace;
-    color: var(--accent);
+    color: #4ade80;
 }
 .step-plate .field {
     color: var(--text-muted);