Diagram: fix label/arrow overlaps

Specific overlaps fixed:
- Output labels (Cluster DB, MSP Library) sat exactly on top of the
  arrow tips coming into the output circles. Moved them BELOW each
  circle (y=+24 relative). Confirmed clear of the bottom legend boxes
  horizontally — outputs are at x=310/590, legends at x=60-260/640-860.
- Parallel-note captions on every step were sitting either above the
  box (in the path of the incoming arrow) or right on top of the red
  shadow stack. Moved each one to the right of its box+shadow at the
  box's vertical center, with a strict 10px clear margin from the
  rightmost shadow edge.
- Per-source row notes (× partitions / × projects) shifted to x=280
  and x=665 respectively (clear of EXTRACT_REPS_DAT shadow at x=267
  and PARQUET_TO_DAT shadow at x=652).
- Spine notes shifted to x=565 (boxes end at x=540, shadows at x=550),
  and the deeper RUN_MARACLUSTER_DAT note to x=585 (shadow at x=558).
- BUILD_CLUSTER_DB / GENERATE_MSP_FORMAT notes shifted to (425, 858)
  and (700, 858) respectively, clear of the wider tail boxes.

Other:
- Extended the partition container down to y=930 so it visibly wraps
  BUILD/MSP (which also run per partition).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: ypriverol