feat(curriculum): add RootNode learning path, student roster, and scenario isolation metadata

Pre-Phase-1 platform work, approved and tested earlier but not yet committed:

- Terminal banner: "RootNode Academy Lab — node: k8s-lab", upstream KubeKosh
  attribution left untouched in footer/README/LICENSE.
- RootNode curriculum mode: scenarios/rootnode-path.json (Foundation -> Workloads
  -> Networking -> Configuration -> Troubleshooting -> Real Ops -> Capstone),
  built from existing scenario content grouped by category, no new scenarios
  invented. New GET /api/curriculum/path endpoint.
- Student roster + per-student progress: instructor-roster, pick-your-name login
  (no password), students/environments-adjacent progress table migrated to a
  (student_id, scenario_id) composite key so practice progress and exam sessions
  are isolated per student instead of one global bucket. New /api/roster,
  /api/login endpoints.
- scenarios/data/*.json: added isolation_type metadata (shared_namespace vs
  ephemeral_cluster) from an audit of which scenarios execute cluster-scoped or
  node-level commands. This was Tier-1-isolation groundwork that got superseded
  same-day by the full-ephemeral-per-student architecture (see
  docs/LAB_ARCHITECTURE.md) — the field is kept as descriptive metadata only,
  per the note now in scenarios/SCHEMA.md. Not wasted: it's an accurate audit of
  which scenarios touch cluster-scoped resources, useful independent of isolation
  model.
- .gitignore added (node_modules/, frontend/dist/, *.db, /data/, .env) — none
  existed before; without it, npm installs during testing would have landed in
  a commit.

Known limitation still open: no frontend UI for any of this yet (login screen,
roster-add form, curriculum view) — API-only. No auth on the roster-add endpoint.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

scenarios/data/limitrange-task.json

@@ -2,6 +2,7 @@
   "id": "limitrange-task",
   "title": "LimitRange for Default Container Limits",
   "category": "Workloads & Scheduling",
+  "isolation_type": "shared_namespace",
   "difficulty": "Medium",
   "type": "task",
   "weight": 6,