refactor: explicit Opencode Executor (#188)

* use display and fromStr implementations in ExecutorConfig

(cherry picked from commit 115a6a447d9195d28b9c29004fa6301fb60b1b89)
(cherry picked from commit 25d589d54a3fc89f8868f5c409f25bdb162f1326)

* rename opencode to charm/opencode

(cherry picked from commit 41fe88a46cc6c7a1cbf5ecbc3599639351c415c8)

* rename opencode on the frontend

* resuse executor types on the frontend

* put back missing types

frontend/src/components/OnboardingDialog.tsx

@@ -81,9 +81,7 @@ export function OnboardingDialog({ open, onComplete }: OnboardingDialogProps) {
                 <Label htmlFor="executor">Default Executor</Label>
                 <Select
                   value={executor.type}
-                  onValueChange={(value: 'echo' | 'claude' | 'amp') =>
-                    setExecutor({ type: value })
-                  }
+                  onValueChange={(value) => setExecutor({ type: value as any })}
                 >
                   <SelectTrigger id="executor">
                     <SelectValue placeholder="Select your preferred coding agent" />
@@ -100,6 +98,8 @@ export function OnboardingDialog({ open, onComplete }: OnboardingDialogProps) {
                   {executor.type === 'claude' && 'Claude Code from Anthropic'}
                   {executor.type === 'amp' && 'From Sourcegraph'}
                   {executor.type === 'gemini' && 'Google Gemini from Bloop'}
+                  {executor.type === 'charmopencode' &&
+                    'Charm/Opencode AI assistant'}
                   {executor.type === 'echo' &&
                     'This is just for debugging vibe-kanban itself'}
                 </p>

frontend/src/components/tasks/TaskDetailsToolbar.tsx

@@ -4,6 +4,7 @@ import { Button } from '@/components/ui/button';
 import { useConfig } from '@/components/config-provider';
 import { attemptsApi, projectsApi } from '@/lib/api';
 import type { GitBranch, TaskAttempt } from 'shared/types';
+import { EXECUTOR_TYPES, EXECUTOR_LABELS } from 'shared/types';
 import {
   TaskAttemptDataContext,
   TaskAttemptLoadingContext,
@@ -16,13 +17,10 @@ import CreatePRDialog from '@/components/tasks/Toolbar/CreatePRDialog.tsx';
 import CreateAttempt from '@/components/tasks/Toolbar/CreateAttempt.tsx';
 import CurrentAttempt from '@/components/tasks/Toolbar/CurrentAttempt.tsx';
 
-const availableExecutors = [
-  { id: 'echo', name: 'Echo' },
-  { id: 'claude', name: 'Claude' },
-  { id: 'amp', name: 'Amp' },
-  { id: 'gemini', name: 'Gemini' },
-  { id: 'opencode', name: 'OpenCode' },
-];
+const availableExecutors = EXECUTOR_TYPES.map((id) => ({
+  id,
+  name: EXECUTOR_LABELS[id] || id,
+}));
 
 function TaskDetailsToolbar() {
   const { task, projectId } = useContext(TaskDetailsContext);