Address reviewer follow-ups: powerProfile detect, slider live-value, glyphs

- powerProfile now hides on machines without power-profiles-daemon by
  checking against the published profile set rather than a never-undefined
  enum, and uses mdi-scale-balance for Balanced (not battery-charging).
- networkPanel renames the QML-keyword-shadowing 'signal' property to
  'signalStrength'; ethernet glyph corrected to mdi-ethernet (not the
  access-point icon).
- workspacesPro indicator color guards against null bar during construction.
- Common.Slider keeps an internal liveValue so external value bindings
  survive a drag; sliders fed from PipeWire/brightnessctl now follow
  external changes after the user interacts.
- audioPanel drops the redundant default-sink PwObjectTracker since the
  candidate-sinks tracker already covers it.
- networkPanel guards scan/connect commands against re-entry while the
  previous Process is running.
- notificationCenter only instantiates its NotificationServer when the
  module is opted in via settings.replaceMako (default off) so it does
  not collide with mako out of the box.
- PopupCard fully opaque while open (previously 0.98) — removes a
  visible ghost outline on first render.
- Drop dead code: calendar trailing MouseArea, weatherFlyout's unused
  parseForecast/forecast property, idleInhibitor's holdSeconds,
  media's scrollAnim.position; gate media's scroll animation off in
  vertical bar mode.

default/quickshell/bar/widgets/powerProfile.qml

@@ -16,7 +16,7 @@ Item {
 
   readonly property var profileGlyphs: ({
     [PowerProfile.PowerSaver]: "󰌪",
-    [PowerProfile.Balanced]: "󰂄",
+    [PowerProfile.Balanced]: "󰗑",
     [PowerProfile.Performance]: "󰓅"
   })
 
@@ -26,7 +26,7 @@ Item {
     [PowerProfile.Performance]: "Performance"
   })
 
-  readonly property bool available: PowerProfiles.profile !== undefined
+  readonly property bool available: PowerProfiles.hasPerformanceProfile || PowerProfiles.profile === PowerProfile.PowerSaver || PowerProfiles.profile === PowerProfile.Balanced
   readonly property int current: PowerProfiles.profile
 
   visible: available
@@ -70,7 +70,7 @@ Item {
       Repeater {
         model: [
           { profile: PowerProfile.PowerSaver, label: "Power Saver", glyph: "󰌪" },
-          { profile: PowerProfile.Balanced, label: "Balanced", glyph: "󰂄" },
+          { profile: PowerProfile.Balanced, label: "Balanced", glyph: "󰗑" },
           { profile: PowerProfile.Performance, label: "Performance", glyph: "󰓅" }
         ]