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 This was Tier-1-isolation groundwork that got superseded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/SCHEMA.md

@@ -53,6 +53,7 @@ Scenarios are defined as JSON objects. A scenario can be either a hands-on conso
   "id": "unique-kebab-case-id",        // string — unique scenario identifier
   "title": "Human-readable Title",      // string — shown in sidebar list
   "category": "Workloads",             // string — groups scenarios in sidebar accordion
+  "isolation_type": "shared_namespace", // "shared_namespace" | "ephemeral_cluster" — see below
   "difficulty": "Easy",                // "Easy" | "Medium" | "Hard"
   "type": "task",                      // "task" | "mcq"
   "weight": 7,                         // number — points value (used for final grade scoring)
@@ -66,6 +67,18 @@ Scenarios are defined as JSON objects. A scenario can be either a hands-on conso
 
 ---
 
+### `isolation_type` — informational, not a security boundary
+
+Earlier draft of this schema used `isolation_type` (`shared_namespace` | `ephemeral_cluster`)
+to decide which scenarios could safely run under shared-cluster RBAC. That namespace-isolation
+approach was superseded before it shipped — see `docs/LAB_ARCHITECTURE.md`. Every student now
+gets a fully separate disposable environment with its own nested cluster, so no scenario
+content is unsafe for any other student's environment; the field no longer gates anything.
+It's kept on scenario records as descriptive metadata only (which scenarios exercise
+cluster-scoped/node-level operations), not read by any authorization logic.
+
+---
+
 ### Hints Schema
 Each hint is rendered as a collapsible card inside the Hints tab of the UI:
 ```jsonc
@@ -149,6 +162,7 @@ Renders a questionnaire block. No terminal is shown. The user answers by selecti
   "id": "scale-deployment",
   "title": "Scale a Deployment",
   "category": "Workloads",
+  "isolation_type": "shared_namespace",
   "difficulty": "Easy",
   "type": "task",
   "weight": 4,
@@ -187,6 +201,7 @@ Renders a questionnaire block. No terminal is shown. The user answers by selecti
   "id": "service-types-mcq",
   "title": "Kubernetes Service Types",
   "category": "Networking",
+  "isolation_type": "shared_namespace",
   "difficulty": "Easy",
   "type": "mcq",
   "weight": 3,