docs: regenerate notebook diagrams with the modernized dj.Diagram style

[dimitri-yatsenko]

Regenerates the diagram assets embedded in the tutorial/how-to notebooks to match the modernized dj.Diagram rendering (datajoint/datajoint-python#1532).

What

Re-executed all 24 notebooks under src/tutorials and src/how-to against the restyled dj.Diagram, refreshing their stored outputs in place (mkdocs-jupyter runs with execute: false, so outputs live in the committed .ipynb). Embedded diagram SVGs now carry:

• the modern tier palette (Lookup as a gray Manual-sized rectangle; Imported/Computed ellipses; near-white part boxes),
• rounded node corners + rounded schema clusters, master-part entity grouping,
• the corrected edge-weight = cardinality rule (thick = 1:1, thin = multi-valued),
• Helvetica typography.

All 24 executed successfully on MySQL (0 failures), including the domain tutorials.

Depends on

datajoint/datajoint-python#1532 (the restyle). This PR should land after #1532 is released, so the rendered diagrams match a shipped dj.Diagram. Re-executing also refreshes non-diagram outputs (this is a full notebook re-run), which is expected for a regeneration pass.

Not included

The .cache/ directory (pooch-downloaded domain datasets) is intentionally not committed.

[dimitri-yatsenko]

⚠️ Regenerate against the final datajoint-python #1534 before merging. These notebook diagrams were rendered from an earlier build of #1534. Since then #1534 gained the auto default theme (adaptive light/dark SVG) and sans-serif schema labels, so the currently-committed SVGs are stale (light-only, Times schema labels). Re-run scripts/execute_notebooks.py against the released/final #1534 to refresh — a single final regeneration, not per intermediate change.