Route Planner speed training

21/21 correct; first Route Planner PB 7.361s→5.621s. Fastest change: stop generic shortest-path reasoning and use the fixed shell—map AB/AC/AD/BC/BD/CE/DE, collapse C=min(AC,AB+BC)+CE and D=min(AD,AB+BD)+DE, then emit the cheaper path with lex tie-break. Four-candidate lex-order variant did not beat PB. Bottleneck: runtime variance.