Go envelope v1.158 — canonical faces-only mark

Replaces the approximate compact logo with a faithful vector trace of the supplied canonical Janus faces.

• removes the visible separator rule and JANUS wordmark from compact placements
• preserves the exact dual-face silhouette with teal/amber coloring
• adds transparent edge padding for clean antialiasing
• keeps the original full PNG unchanged as the canonical reference
• uses the SVG consistently in the sidebar, auth header, and favicon