feat(ci): add health dashboard Space + benchmark metrics artifacts

- spaces/health-dashboard/app.py: Gradio Space that queries the GitHub
  Actions API directly (no extra datastore). Shows benchmark status
  badges, success-rate and duration trend charts, and embeds the latest
  rollout video per benchmark. Results cached 5 min in-memory; video
  files cached on disk by artifact ID so downloads only happen once.
- spaces/health-dashboard/requirements.txt + README.md: Space card with
  setup instructions for the GITHUB_RO_TOKEN secret (actions:read,
  metadata:read only).
- scripts/ci/parse_eval_metrics.py: runs on the CI host after each eval,
  reads eval_info.json written by lerobot-eval, extracts pc_success and
  n_episodes, and writes metrics.json to the artifacts dir.
- .github/workflows/benchmark_tests.yml: add "Parse … metrics" and
  "Upload … metrics" steps (if: always()) after each eval so the
  dashboard has data even when the eval fails.

The Space should be deployed as a private Space under the huggingface
org. Required secret: GITHUB_RO_TOKEN (fine-grained, read-only).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

spaces/health-dashboard/README.md

@@ -0,0 +1,27 @@
+---
+title: LeRobot Health Dashboard
+emoji: 🤖
+colorFrom: yellow
+colorTo: orange
+sdk: gradio
+sdk_version: 5.29.0
+app_file: app.py
+pinned: true
+license: apache-2.0
+short_description: Live CI health for the LeRobot main branch
+---
+
+# LeRobot Health Dashboard
+
+Internal dashboard for monitoring the health of the `main` branch — benchmark smoke-test
+success rates, CI job durations, and latest rollout videos, all pulled live from the
+GitHub Actions API.
+
+## Required secret
+
+Add `GITHUB_RO_TOKEN` in the Space settings with a fine-grained GitHub token scoped to:
+
+- **Repository**: `huggingface/lerobot`
+- **Permissions**: `Actions` → Read-only, `Metadata` → Read-only
+
+The token is never exposed in the UI or logs.