feat: add Files tab for browsing workspace files (#154)

* feat: add Files tab for browsing workspace files

- Add Files tab between Diff and Terminal in header
- Implement hierarchical file tree with expand/collapse
- Add fuzzy search with debouncing and relevance ranking
- Support gitignore filtering via `git check-ignore` (web + desktop)
- Add syntax highlighting for 150+ file types
- Add image preview (SVG, PNG, JPG, etc.)
- Add line numbers, wrap toggle, and copy button
- Desktop: split-pane layout matching DiffView
- Mobile: drill-in navigation with full-width sidebar
- Update help dialog with Cmd+3 shortcut
- Increase header breakpoint to 940px for new tab

* feat: enhance context and session stores to track agent/model/variant choices for historical sessions

* feat: implement line selection and commenting functionality in FilesView

packages/ui/src/lib/opencode/client.ts

@@ -1703,7 +1703,7 @@ class OpencodeService {
     return result;
   }
 
-  async listLocalDirectory(directoryPath: string | null | undefined): Promise<FilesystemEntry[]> {
+  async listLocalDirectory(directoryPath: string | null | undefined, options?: { respectGitignore?: boolean }): Promise<FilesystemEntry[]> {
     const desktopFiles = getDesktopFilesApi();
     if (desktopFiles) {
       try {
@@ -1729,6 +1729,9 @@ class OpencodeService {
       if (directoryPath && directoryPath.trim().length > 0) {
         params.set('path', directoryPath);
       }
+      if (options?.respectGitignore) {
+        params.set('respectGitignore', 'true');
+      }
       const query = params.toString();
       const response = await fetch(`${this.baseUrl}/fs/list${query ? `?${query}` : ''}`);
       if (!response.ok) {