Fixes#43
- Two-entity constraints (parallel, tangent, equal, ...) get a glyph on each entity.
- Glyphs sit beside their entity (offset along its screen normal), step along it when crowded,
with a faint leader when pushed away; 15 px boxes with the toolbar's constraint icons
(H/V stay letters), coloured from the theme's glyph tokens in both themes.
- Hovering a glyph lights both of its glyphs and its curves/points and names the constraint.
- Removes the old duplicate glyph drawer in viewport.rs (it drew a second, green set).
- Scenario expect key `glyphs` ({constraint id: count}, none overlapping) and the scenario
constraint_glyphs_both_entities.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RjGw4gA5ZvKrU8MQP6sBgT