Replace worker initials with clearer ambient worker visuals

[joryirving]

Summary

Replace or augment tile initials with more readable worker visuals.

Why

The colony should feel alive at a glance while multitasking. Initials in grid cells communicate state, but they do not yet feel like tiny people inhabiting the desktop.

Scope

• Add simple worker visuals appropriate for a compact overlay
• Preserve readability at small sizes
• Make it easier to track worker movement and occupation without reading text

Acceptance Criteria

• Worker presence is visually obvious without relying only on initials
• The visuals remain readable at dock size
• Movement and occupancy are easier to follow