Consolidate omarchy-shell colors into a single shell.toml surface

Five plugins each owned their own colors.toml watcher with subtly
different parsers, plus two ad-hoc per-theme override files
(notifications.json, image-picker-colors.json). This collapses all of
that into one source of truth: Commons/Color.qml watches colors.toml +
shell.toml and exposes Color.bar.*, Color.popups.*, Color.notifications.*,
Color.menu.*, Color.imagePicker.* for every surface to bind to.

shell.toml is generated by the existing template pipeline from
default/themed/shell.toml.tpl. Themes can ship their own shell.toml to
override individual keys; everything missing falls back to the
foundational palette via root.pick(). Settings panel is intentionally
not themable beyond the foundational tokens.

last-horizon and solitude ship a minimal shell.toml to preserve their
historical 'notification border matches Hyprland active border'
behavior, which previously came from parsing the theme's hyprland.conf
(now removed).

default/quickshell/omarchy-shell/plugins/notifications/Service.qml

@@ -33,17 +33,6 @@ Item {
   readonly property string cacheDir: home + "/.cache/omarchy/"
   readonly property string imageCacheDir: cacheDir + "notification-images/"
   readonly property string styleStatePath: home + "/.local/state/omarchy/toggles/quickshell-menu.json"
-  // Optional per-theme override file. Themes that want notification colors
-  // to diverge from the rest of the palette can ship this file. Schema:
-  //   {
-  //     "borderColor":     "#hex",
-  //     "backgroundColor": "#hex",
-  //     "textColor":       "#hex",
-  //     "countdownColor":  "#hex"   // progress bar at bottom of popup
-  //   }
-  // All keys optional; unset keys fall back to the live Color.* tokens.
-  readonly property string themeOverridePath: home + "/.config/omarchy/current/theme/notifications.json"
-  readonly property string themeNamePath: home + "/.config/omarchy/current/theme.name"
 
   // Corner radius is shared with omarchy-shell menu and settings panel —
   // `omarchy style corners <sharp|round>` writes this file once and every
@@ -78,57 +67,6 @@ Item {
     onFileChanged: reload()
   }
 
-  // ----------------------------------------------- per-theme color overrides
-
-  property string overrideBorder: ""
-  property string overrideBackground: ""
-  property string overrideText: ""
-  property string overrideCountdown: ""
-
-  // Match the compact mako-style layout, but keep colors live-bound to the
-  // current Omarchy theme unless a theme explicitly ships notifications.json.
-  readonly property color effectiveBorder: overrideBorder.length > 0 ? overrideBorder : Color.accent
-  readonly property color effectiveBackground: overrideBackground.length > 0 ? overrideBackground : Color.background
-  readonly property color effectiveText: overrideText.length > 0 ? overrideText : Color.foreground
-  readonly property color effectiveCountdown: overrideCountdown.length > 0 ? overrideCountdown : Color.accent
-
-  function loadThemeOverride(raw) {
-    try {
-      var parsed = JSON.parse(raw || "{}")
-      overrideBorder = typeof parsed.borderColor === "string" ? parsed.borderColor : ""
-      overrideBackground = typeof parsed.backgroundColor === "string" ? parsed.backgroundColor : ""
-      overrideText = typeof parsed.textColor === "string" ? parsed.textColor : ""
-      overrideCountdown = typeof parsed.countdownColor === "string" ? parsed.countdownColor : ""
-    } catch (e) {
-      overrideBorder = ""
-      overrideBackground = ""
-      overrideText = ""
-      overrideCountdown = ""
-    }
-  }
-
-  FileView {
-    id: themeOverrideFile
-    path: service.themeOverridePath
-    watchChanges: true
-    printErrors: false
-    onLoaded: service.loadThemeOverride(text())
-    onLoadFailed: service.loadThemeOverride("")
-    onFileChanged: reload()
-  }
-
-  // Theme switching recreates ~/.config/omarchy/current/theme, which can leave
-  // the notifications.json watcher attached to the old symlink target. Watch
-  // theme.name (overwritten in place) as the stable tripwire and force a fresh
-  // override reload; if the new theme has no override, onLoadFailed clears the
-  // old colors instead of leaving stale theme-specific notification styling.
-  FileView {
-    path: service.themeNamePath
-    watchChanges: true
-    printErrors: false
-    onFileChanged: themeOverrideFile.reload()
-  }
-
   // Fired by IPC (`omarchy-shell-ipc notifications showHistory`) so the
   // bar widget can drop its PopupCard from the same anchor a click would.
   signal historyOpenRequested()
@@ -948,10 +886,6 @@ Item {
               urgency: cardSlot.urgency
               timestamp: cardSlot.timestamp
               cornerRadius: service.cornerRadius
-              borderColorOverride: service.effectiveBorder
-              backgroundColorOverride: service.effectiveBackground
-              textColorOverride: service.effectiveText
-              countdownColorOverride: service.effectiveCountdown
               fontFamily: service.shell && service.shell.bar ? service.shell.bar.fontFamily : ""
               glyph: cardSlot.glyph
               progress: cardSlot.progress