feat(FN-903): add middle truncation utility for file paths in dashboard

- Add truncatePath utility function with configurable segments and placeholder
- Apply middle truncation to file paths in ChangedFilesModal sidebar
- Apply middle truncation to file paths in TaskChangesTab
- Remove unused CSS truncation styles replaced by the new utility
- Add comprehensive test suite for truncatePath (106 tests)

packages/dashboard/app/components/ChangedFilesModal.tsx

@@ -10,6 +10,7 @@ import {
 } from "lucide-react";
 import { useChangedFiles } from "../hooks/useChangedFiles";
 import { highlightDiff } from "../utils/highlightDiff";
+import { truncateMiddle } from "../utils/truncatePath";
 import type { TaskFileDiff } from "../api";
 
 const MOBILE_BREAKPOINT = 768;
@@ -237,7 +238,7 @@ export function ChangedFilesModal({
                       onClick={() => handleSelectFile(file)}
                     >
                       <span className="file-node-icon">{getStatusIcon(file.status)}</span>
-                      <span className="file-node-name">{file.path}</span>
+                      <span className="file-node-name" title={file.path}>{truncateMiddle(file.path)}</span>
                       <span className={`detail-column-badge changed-files-badge changed-files-badge--${file.status}`}>
                         {getStatusLabel(file.status)}
                       </span>

packages/dashboard/app/components/TaskChangesTab.tsx

@@ -3,6 +3,7 @@ import { FileCode, ChevronDown, ChevronRight, AlertCircle, GitCommit } from "luc
 import type { MergeDetails, Column } from "@fusion/core";
 import { fetchTaskDiff, type TaskDiff } from "../api";
 import { highlightDiff } from "../utils/highlightDiff";
+import { truncateMiddle } from "../utils/truncatePath";
 
 interface TaskChangesTabProps {
   taskId: string;
@@ -214,7 +215,7 @@ export function TaskChangesTab({ taskId, worktree, projectId, column, mergeDetai
                   {getStatusLabel(file.status)}
                 </span>
                 <span className="changes-file-path" title={file.path}>
-                  {file.path}
+                  {truncateMiddle(file.path)}
                 </span>
                 <span
                   className="changes-file-stat"