docs: address tutorial review feedback (quickstart, personas, E2E story)

[geoHeil]

Resolves the tutorial review feedback on #1 (see the review comment). Text-only; no images or links touched.

Mapping to the review points:

1. Quickstart buried → 3-line git clone && pixi run start block now sits in the intro, with a pointer to Running it for the docker/HPC modes.
2. Beginner promise implicit → new intro paragraph contrasting the manual login-node/module load/scattered-logs workflow with the version-locked, auto-packed, button-in-the-UI one, including the close-your-laptop/reattach behavior.
3. Local mode partial coverage → local mode section now names the three assets that materialize locally and carries a {note} admonition stating the three that fail at import time and why.
4. Expectations → corpus download stated as ~8 MB (verified: the archive is 8.2 MB); first staging run dominated by env packing, warm-cache full chain in minutes.
5. Queue-wait / sessions → fan-out section now names the fifteen-queue-waits trade-off and points to run-scoped Slurm allocations (Choose an execution mode).
6. Multi-cluster → real-HPC section now states that separate deployments/code locations can target more than one cluster, linking the Leonardo and VSC-5 guides.
7. E2E story stops at Slurm → new HPC in the middle, Dagster end to end subsection: everything is sbatch here by choice; before/after stages can be ordinary local assets in the same lineage graph; compute nodes often lack internet, so a download stage would move off-cluster in production.
8. Iteration loop → folded into the new intro paragraph (identical code, seconds-scale local iteration — for you or your coding agent — promoted unchanged to the cluster).
9. topic_map screenshot promised but absent → sentence softened to "(not shown above — materialize the group and open topic_map to see it)".

Validation: notebook JSON round-trips (6 cells, no formatting churn — 4 lines changed), codespell clean, all newly added links return 200.

🤖 Generated with Claude Code