refactor(maestro): drop per-session colour and pane glow

The sidebar row dot, the pane top strip and the mobile pill dot all
painted a hashed per-session colour; the focused pane added an outer
accent glow on top of its ring. Removes the colour concept entirely
along with the glow, leaving the flat accent ring as the only focus mark.

web/src/styles.css

@@ -2301,20 +2301,10 @@ input.leaf-rename:focus {
   min-width: 0;
   min-height: 0;
 }
-/* per-session colour strip — maps a pane to its sidebar row */
-.mv-pane::before {
-  content: "";
-  position: absolute;
-  inset: 0 0 auto 0;
-  height: 2px;
-  background: var(--mv-color, transparent);
-  z-index: 3;
-  pointer-events: none;
-}
-/* focused pane: accent ring + glow, full strength */
+/* focused pane: accent ring, full strength */
 .mv-pane.is-focused {
   border-color: var(--accent);
-  box-shadow: inset 0 0 0 1px var(--accent), 0 0 22px -8px var(--accent-ring);
+  box-shadow: inset 0 0 0 1px var(--accent);
 }
 /* unfocused panes recede so the eye finds the live one */
 .mv-pane:not(.is-focused) {
@@ -2417,31 +2407,12 @@ input.leaf-rename:focus {
   border-radius: var(--r-1);
 }
 
-/* sidebar two-tier highlight + colour dot (issue #33).
+/* sidebar two-tier highlight (issue #33).
    .is-active = focused pane (loud, from existing rule); .is-open = open
-   elsewhere (quiet). The dot uses the session's colour so a row maps to a pane. */
+   elsewhere (quiet). */
 .tree-leaf.is-open {
   background: color-mix(in oklab, var(--accent) 6%, transparent);
 }
-.tree-leaf.is-open::after,
-.tree-leaf.is-active::after {
-  content: "";
-  position: absolute;
-  right: 9px;
-  top: 50%;
-  width: 7px;
-  height: 7px;
-  margin-top: -3.5px;
-  border-radius: 50%;
-  background: var(--mv-color, var(--accent));
-  pointer-events: none;
-}
-.tree-leaf.is-open::after {
-  opacity: 0.7;
-}
-.tree-leaf.is-active::after {
-  box-shadow: 0 0 8px var(--mv-color, var(--accent-ring));
-}
 
 /* =========================================================================
    multi-view mobile (#35): below 860px the split tree projects to a pill strip
@@ -2486,14 +2457,6 @@ input.leaf-rename:focus {
   cursor: pointer;
   border: 1px solid transparent;
 }
-.mv-pill::before {
-  content: "";
-  width: 7px;
-  height: 7px;
-  border-radius: 50%;
-  background: var(--mv-color, var(--faint));
-  flex: none;
-}
 .mv-pill.is-active {
   background: var(--accent-tint);
   color: var(--accent-strong);