Epic: Planner clarity & buildability

[ApocDev]

Make solved plans easier to understand and translate into a physical factory. This covers first-class material-link inspection, train payload/cadence guidance, and explicit route-feasibility analysis outside the production LP.

Sub-issues:

• Make material links inspectable and directly editable #149 — inspect and edit material links directly.
• Train logistics: payload and cadence math on factory links #102 — train payload and cadence math on factory links.
• Build-side logistics: assess belt and pipe route feasibility #148 — assess belt and pipe route feasibility.

Order: ship link clarity first, then bounded train math, then the research-heavy route model. Route feasibility must define its supported layout assumptions and feasible/impossible/unknown boundary before implementation.