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/lib/opencode/client.ts

@@ -664,6 +664,28 @@ class OpencodeService {
     return response.data;
   }
 
+  async forkSession(sessionId: string, messageId?: string): Promise<Session> {
+    const baseUrl = this.baseUrl.replace(/\/$/, '');
+    const url = new URL(`/api/session/${sessionId}/fork`, baseUrl);
+
+    if (this.currentDirectory) {
+      url.searchParams.set('directory', this.currentDirectory);
+    }
+
+    const response = await fetch(url.toString(), {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify(messageId ? { messageID: messageId } : {}),
+    });
+
+    if (!response.ok) {
+      const text = await response.text();
+      throw new Error(`Failed to fork session: ${text || response.statusText}`);
+    }
+
+    return response.json();
+  }
+
   async getSessionStatus(): Promise<
     Record<string, { type: "idle" | "busy" | "retry"; attempt?: number; message?: string; next?: number }>
   > {