feat(ui): accent color presets in Settings → General

Adds Moss / Peat / Sea preset swatches to the General settings tab.
Selecting a preset mutates the live SolidColorBrush objects in the
Application resource dictionary so all StaticResource consumers update
instantly; the choice is persisted to ui.config.json and re-applied
at startup. Missing or unknown saved value falls back to Moss.

src/ClaudeDo.Localization/locales/en.json

@@ -31,7 +31,11 @@
       "weekdayFriday": "Friday",
       "weekdaySaturday": "Saturday",
       "sessionSkills": "Session skills",
-      "sessionSkillsHint": "Applied to every task. Combines with list- and task-level selections."
+      "sessionSkillsHint": "Applied to every task. Combines with list- and task-level selections.",
+      "accentPreset": "Accent color",
+      "accentPresetMoss": "Moss",
+      "accentPresetPeat": "Peat",
+      "accentPresetSea": "Sea"
     },
     "worktrees": {
       "strategy": "Strategy",