feat: implement work mode selection in feature dialogs

- Added WorkModeSelector component to allow users to choose between 'current', 'auto', and 'custom' work modes for feature management.
- Updated AddFeatureDialog and EditFeatureDialog to utilize the new work mode functionality, replacing the previous branch selector logic.
- Enhanced useBoardActions hook to handle branch name generation based on the selected work mode.
- Adjusted settings to default to using worktrees, improving the overall feature creation experience.

These changes streamline the feature management process by providing clearer options for branch handling and worktree isolation.

apps/ui/src/components/views/settings-view/feature-defaults/feature-defaults-section.tsx

@@ -358,9 +358,6 @@ export function FeatureDefaultsSection({
             >
               <GitBranch className="w-4 h-4 text-brand-500" />
               Enable Git Worktree Isolation
-              <span className="text-[10px] px-1.5 py-0.5 rounded-md bg-amber-500/15 text-amber-500 border border-amber-500/20 font-medium">
-                experimental
-              </span>
             </Label>
             <p className="text-xs text-muted-foreground/80 leading-relaxed">
               Creates isolated git branches for each feature. When disabled, agents work directly in