fix: robust annotation legends

[Sergio-ote]

What & why

Annotation legends formerly overlapped with adjacent plots whenever cell type labels were too wordy. Multiple panel grids have been reorganized, so legends are now displayed in an independent row to avoid collisions.

An extra fix on the clustree and silhouette plots was also added, since not all leiden resolutions were previously displayed, and silhouette plots did not fully match clustering colors when the number of clusters was >10.

Validation

• Workflow lint passes against .test/
• Decoupled .test/ dry-run builds the CoreBlock DAG
• Affected HeadBlock mode was dry-run with a complete mode-specific config and representative inputs, if applicable
• Config validates against workflow/schemas/config.schema.yaml
• mkdocs build --strict passes, if documentation was changed
• Catalogue rule graph was generated before a release, if applicable
• Parameter names match between .smk rules and scripts; documentation was updated if behaviour changed