feat(workspaces): add workspace sessions and management

Introduce workspace support to group repositories and store per-workspace
open tabs and the last active repository. Integrate a workspace picker into
the repository tab bar and add workspace controls to the dashboard to
create, edit, switch and delete workspaces. Persist and migrate workspace
preferences robustly and include tests for migration, corruption and edge
cases.

- Persist per-workspace sessions and active repo to localStorage
- Add workspace picker in tabs and dashboard management hooks
- Include migration/validation logic and unit tests for edge cases

src/lib/workspaces.ts

@@ -0,0 +1,42 @@
+export interface Workspace {
+  id: string;
+  name: string;
+  repositories: string[];
+  openPaths: string[];
+  activePath: string;
+}
+export interface WorkspaceState {
+  selectedId: string;
+  workspaces: Workspace[];
+  defaultSession: { openPaths: string[]; activePath: string };
+}
+export const WORKSPACES_KEY = "gitlite.workspaces.v1";
+const paths = (value: unknown): string[] => Array.isArray(value)
+  ? [...new Set(value.filter((path): path is string => typeof path === "string" && !!path.trim()))] : [];
+export function readWorkspaces(storage: Pick<Storage, "getItem">, openPaths: string[]): WorkspaceState {
+  const fallback: WorkspaceState = { selectedId: "", workspaces: [], defaultSession: { openPaths, activePath: "" } };
+  try {
+    const raw = storage.getItem(WORKSPACES_KEY);
+    if (raw) {
+      const saved = JSON.parse(raw);
+      const workspaces: Workspace[] = Array.isArray(saved.workspaces) ? saved.workspaces.flatMap((item: any) => {
+        if (!item || typeof item.id !== "string" || !item.id.startsWith("workspace-") || typeof item.name !== "string" || !item.name.trim()) return [];
+        const repositories = paths(item.repositories);
+        const openPaths = paths(item.openPaths).filter(path => repositories.includes(path));
+        return [{ id: item.id, name: item.name, repositories, openPaths,
+          activePath: openPaths.includes(item.activePath) ? item.activePath : openPaths[0] ?? "" }];
+      }) : [];
+      const defaultPaths = paths(saved.defaultSession?.openPaths);
+      return { workspaces, selectedId: workspaces.some(item => item.id === saved.selectedId) ? saved.selectedId : "",
+        defaultSession: { openPaths: defaultPaths, activePath: defaultPaths.includes(saved.defaultSession?.activePath) ? saved.defaultSession.activePath : defaultPaths[0] ?? "" } };
+    }
+    const legacy = JSON.parse(storage.getItem("gitty.dashboard.v1") ?? "{}");
+    if (Array.isArray(legacy.workspaces)) fallback.workspaces = legacy.workspaces.flatMap((item: any) => {
+      if (!item || typeof item.id !== "string" || !item.id.startsWith("workspace-") || typeof item.name !== "string" || !item.name.trim()) return [];
+      const repositories = Object.entries(legacy.assignments ?? {}).filter(([, id]) => id === item.id).map(([path]) => path);
+      const tabs = openPaths.filter(path => repositories.includes(path));
+      return [{ ...item, repositories, openPaths: tabs, activePath: tabs[0] ?? "" }];
+    });
+  } catch { /* Invalid optional preferences must not block startup. */ }
+  return fallback;
+}