Task 163: Transfer Leg → Episode Navigation Links

Status: DONE

Motivation

The full-route orbital diagram in the cross-episode summary page has interactive leg highlighting (Task 162). When a user hovers/clicks a transfer leg, they see a tooltip with the leg label. However, there's no way to navigate from a leg to the corresponding episode analysis page.

This is the remaining enhancement from ideas/full_route_enhancements.md:

> Leg highlighting could include episode navigation links (click a leg → go to that episode's analysis)

Goal

Add clickable episode navigation links to transfer leg tooltips. When a user clicks a transfer leg in the full-route diagram, the tooltip shows both the leg label and a "→ 第N話分析" link that navigates to the corresponding episode page.

Approach

1. Add data-leg-episode attribute to <g class="transfer-leg"> groups in the SVG renderer
2. Parse episode number from the transfer arc label (e.g., "EP1: ..." → episode 1)
3. Update tooltip in orbital-animation.js to render an HTML link when episode data is available
4. Add tests for the new attributes and tooltip behavior

Dependencies

• Task 162 (leg highlighting — DONE)