feat: implement Undo/Redo/Timeline and Fork Features and fixed opencode.json reading issue on broken json (#99)

* feat: add /undo, /redo, /timeline slash commands and fork button

- Add /undo command to revert to previous user message
- Add /redo command to redo previously undone messages
- Add /timeline command to show conversation history
- Add fork button on user messages (hover) to create new session
- Add TimelineDialog component for navigating conversation history
- Show undo/redo/timeline in autocomplete when session exists
- Fix fork to use SDK session.fork API
- Silent no-op behavior for undo/redo when no messages (matches OpenCode CLI)

* fix: correct fork session endpoint and session switching

- Add hybrid SDK approach using v1 for existing methods and v2 for fork only
- v2 SDK has correct endpoint /session/{sessionID}/fork instead of broken /session/{id}/fork
- Fix forkFromMessage to use setCurrentSession instead of direct set
- Ensures both useSessionStore and useSessionManagementStore are consistent
- Fixes issue where forked sessions appeared empty until sending a new message

* fix: use direct fetch for fork to avoid v2 SDK build errors

- Remove v2 SDK imports and hybrid SDK approach
- Use direct fetch() call to /api/session/{sessionID}/fork endpoint
- Avoids type conflicts between v1 and v2 SDK
- Bypasses broken v1 SDK fork endpoint (wrong path parameter)
- All codebase now uses v1 SDK consistently

* fix: use jsonc-parser for config file parsing

- Replace strip-json-comments + JSON.parse with jsonc-parser
- Handles comments, trailing commas, and unquoted keys
- Matches OpenCode CLI config parsing behavior
- Fixes SyntaxError when reading global opencode.json config

* feat: improve timeline dialog with loading state and search

- Add loading spinner on fork button during operation (~30s on big sessions)
- Refresh session list after fork so new session appears in sidebar immediately
- Add search bar to filter messages by prompt text content
- Show 'No messages found' when search has no results
- Disable fork button while forking to prevent duplicate operations

packages/ui/src/components/chat/ChatInput.tsx

@@ -82,7 +82,7 @@ export const ChatInput: React.FC<ChatInputProps> = ({ onOpenSettings, scrollToBo
 
     const { currentProviderId, currentModelId, currentAgentName, setAgent, getVisibleAgents } = useConfigStore();
     const agents = getVisibleAgents();
-    const { isMobile, inputBarOffset, isKeyboardOpen } = useUIStore();
+    const { isMobile, inputBarOffset, isKeyboardOpen, setTimelineDialogOpen } = useUIStore();
     const { working } = useAssistantStatus();
     const [showAbortStatus, setShowAbortStatus] = React.useState(false);
     const abortTimeoutRef = React.useRef<ReturnType<typeof setTimeout> | null>(null);
@@ -355,7 +355,7 @@ export const ChatInput: React.FC<ChatInputProps> = ({ onOpenSettings, scrollToBo
             textareaRef.current?.blur();
         }
 
-        // Handle /summarize command scroll
+        // Handle slash commands locally before sending
         const normalizedCommand = primaryText.trimStart();
         if (normalizedCommand.startsWith('/')) {
             const commandName = normalizedCommand
@@ -363,7 +363,29 @@ export const ChatInput: React.FC<ChatInputProps> = ({ onOpenSettings, scrollToBo
                 .trim()
                 .split(/\s+/)[0]
                 ?.toLowerCase();
-            if (commandName === 'summarize') {
+
+            // NEW: /undo - revert to last message (populates input with reverted message text)
+            if (commandName === 'undo' && currentSessionId) {
+                await useSessionStore.getState().handleSlashUndo(currentSessionId);
+                // Don't clear message - pendingInputText will populate it with reverted message
+                scrollToBottom?.({ instant: true, force: true });
+                return; // Don't send to assistant
+            }
+            // NEW: /redo - unrevert or partial redo (populates input with message text)
+            else if (commandName === 'redo' && currentSessionId) {
+                await useSessionStore.getState().handleSlashRedo(currentSessionId);
+                // Don't clear message - pendingInputText will populate it
+                scrollToBottom?.({ instant: true, force: true });
+                return; // Don't send to assistant
+            }
+            // NEW: /timeline - open timeline dialog
+            else if (commandName === 'timeline' && currentSessionId) {
+                setTimelineDialogOpen(true);
+                setMessage('');
+                return; // Don't send to assistant
+            }
+            // Existing: /summarize command scroll
+            else if (commandName === 'summarize') {
                 scrollToBottom?.({ instant: true, force: true });
             }
         }