feat(FN-4227): add clickable file path links across dashboard

- Add reusable file path linkification utilities and FileBrowser context wiring across dashboard modals and log surfaces
- Linkify task detail, review, workflow, chat, activity, agent, dev server, and settings sync outputs so workspace paths open in the file browser
- Preserve inline code styling when wrapping detected paths and extend FileBrowserModal handling for linked navigation
- Cover the new linking behavior with dashboard tests and add a changeset plus AGENTS guidance for the reusable pattern

Fusion-Task-Id: FN-4227

packages/dashboard/app/hooks/__tests__/useModalManager.test.ts

@@ -204,6 +204,31 @@ describe("useModalManager", () => {
     expect(result.current.detailTaskInitialTab).toBe("definition");
   });
 
+  it.each([
+    [undefined, undefined, null],
+    ["worktree-FN-X", undefined, null],
+    [undefined, "packages/foo/bar.ts", "packages/foo/bar.ts"],
+  ])("opens files modal with workspace %s and initial file %s", (workspace, initialFile, expectedInitialFile) => {
+    const { result } = renderHook(() =>
+      useModalManager({ projectId: "proj_1", planningSessions: [] }),
+    );
+
+    act(() => {
+      result.current.openFiles(workspace, initialFile);
+    });
+
+    expect(result.current.filesOpen).toBe(true);
+    expect(result.current.fileBrowserInitialFile).toBe(expectedInitialFile);
+    expect(result.current.fileBrowserWorkspace).toBe(workspace ?? "project");
+
+    act(() => {
+      result.current.closeFiles();
+    });
+
+    expect(result.current.filesOpen).toBe(false);
+    expect(result.current.fileBrowserInitialFile).toBeNull();
+  });
+
   it("accepts plain Task object in openDetailWithChangesTab", () => {
     const task = createTask("FN-789");
     const { result } = renderHook(() =>