Draw the board as track, split the site into three pages, and fix curve geometry

Adds SVG board rendering shared by the game and the replay, a splash page with a
shareable replay directory, hover tooltips for reference detail, and makes curves
two-port arcs so sidings and run-arounds can finally be built.

src/sim/view.ts

@@ -28,7 +28,7 @@ import {
 import type { Intent } from '../engine/intents.ts';
 import type { Facility, GameState, TrackCard } from '../engine/state.ts';
 import type { TrackGeometry } from '../engine/content.ts';
-import { variantsFor } from '../engine/track.ts';
+import { connectionsFor, variantsFor } from '../engine/track.ts';
 import type { Impediment } from './narrate.ts';
 import { carLabel, clockTime, impediments, phaseLabel } from './narrate.ts';
 
@@ -47,6 +47,12 @@ export type CellView = {
   tray: string | null;
   cars: string[];
   facility: FacilityView | null;
+  /**
+   * The port pairs this card joins, as two-letter codes — 'ew', 'ns', 'es' and so on. Taken from
+   * the engine's own `connectionsFor`, so a drawn rail can never claim a connection the rules do
+   * not have.
+   */
+  links: string[];
   /**
    * What this card DOES, now that it is on the board.
    *
@@ -85,6 +91,11 @@ export type DivisionView = {
   kind: string;
   label: string;
   trains: TrainChip[][];
+  /**
+   * How many trains may stand here, or null for no limit. 1 on most Mainline cards, 2 where the
+   * card prints "trains may pass", the A/D count at an Office, unlimited at a Division Point.
+   */
+  capacity: number | null;
   /** Modifiers laid on a Mainline card (Brakeman, Helpers, Realignment …). */
   modifiers: string[];
   /**
@@ -109,6 +120,8 @@ export type Frame = {
   whereFrom: { row: number; col: number } | null;
   division: DivisionView[];
   cells: CellView[];
+  /** Which grid row is the Running Track — the spine the district hangs beneath. */
+  runningRow: number;
   facilities: FacilityView[];
   hand: string[];
   /** What each hand card does, in the same order — names alone are not a playable hand. */
@@ -392,6 +405,7 @@ export function snapshot(
       label,
       running: row === area.runningRow,
       what: cellDescription(card, officeProfile(area.tier).name, row === area.runningRow),
+      links: connectionsFor(card).map(([a, b]) => `${a}${b}`),
       enhancements: card.enhancements.map(prettyKey),
       tray: trayAt.get(key) ?? null,
       cars: (card.facility?.industryTrack.length ? card.facility.industryTrack.cars : card.standing).map(carLabel),
@@ -405,6 +419,7 @@ export function snapshot(
         kind: 'dp',
         label: n.side === 'west' ? 'West DP' : 'East DP',
         trains: [n.holding.map((id) => trainChip(s, id))],
+        capacity: null,
         modifiers: [],
         gradeUp: null,
       };
@@ -421,6 +436,7 @@ export function snapshot(
           const chip = trainChip(s, t.tray);
           return { ...chip, label: `${chip.label} (${t.stagesRemaining})` };
         })],
+        capacity: MAINLINE_PROFILES.find((m) => m.kind === n.card)?.trainsMayPass ? 2 : 1,
         modifiers: [
           ...(n.modifiers ?? []).map(prettyKey),
           ...(n.absSignals ? ['ABS Signals'] : []),
@@ -432,6 +448,7 @@ export function snapshot(
       kind: 'office',
       label: officeProfile(areaOf(s, n.owner).tier).name,
       trains: [areaOf(s, n.owner).adOccupancy.map((id) => trainChip(s, id))],
+      capacity: officeProfile(areaOf(s, n.owner).tier).adTracks,
       modifiers: [],
       gradeUp: null,
     };
@@ -466,6 +483,7 @@ export function snapshot(
         return { piece: `${hand === 'none' ? '' : hand + '-hand '}${geometryLabel(geometry ?? '')}`, left };
       })
       .sort((a, b) => a.piece.localeCompare(b.piece)),
+    runningRow: area.runningRow,
     blocked: impediments(s, 0),
     trains: [...s.trays.values()].map((t) => ({
       label: t.trainNumber === null ? 'local crew' : `Train ${t.trainIsExtra ? 'X' : ''}${t.trainNumber}`,