Add hq.svg (flag-base command building) and station.svg (shield, rendered
glyph-only over each side's fill) for in-world building icons. Redraw
tunnel_entry.svg as the shared Tunnel build button: the belt runs on the
surface at both ends and drops straight into/out of the ground, with rounded
corners and a single exit tip. No belt/splitter/tunnel world icons.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Y7N59FsLA5e2kuVdqe4Uhc
