Add Lambert solver, transfer matrix, Dijkstra routing, and route planner UI

- Lambert's problem solver using universal variable method with bisection
  (handles elliptic, parabolic, hyperbolic transfers + anti-podal cases)
- Transfer matrix: precompute pairwise station transfers over time window
  using Lambert solver with configurable launch velocity
- Dijkstra routing on time-expanded graph (station × week nodes, transfer
  + wait edges) to find minimum-time routes
- Route Planner UI: from/to station dropdowns, search window selector
  (1-10 years), "Find Optimal Route" button with results card
- Route visualization: orange dashed trajectory lines with arrow heads
  and leg numbers on the 2D canvas
- Tested: Mercury L1 → Jupiter L1 computes 6-month direct transfer at
  30 km/s — physically reasonable

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/lib/render/canvas2d/SolarSystem2D.ts

@@ -20,6 +20,7 @@ export class SolarSystem2DRenderer {
 	private stationPositions: Float64Array = new Float64Array(0);
 	private stationNames: string[] = [];
 	private showStations: boolean = true;
+	private routeLegs: { from: number; to: number }[] = [];
 	private isDragging = false;
 	private lastMouse = { x: 0, y: 0 };
 	private animFrameId: number = 0;
@@ -86,6 +87,10 @@ export class SolarSystem2DRenderer {
 		this.showStations = visible;
 	}
 
+	updateRoute(legs: { from: number; to: number }[]) {
+		this.routeLegs = legs;
+	}
+
 	render() {
 		const { canvas, ctx } = this;
 		const dpr = window.devicePixelRatio || 1;
@@ -133,6 +138,11 @@ export class SolarSystem2DRenderer {
 			}
 		}
 
+		// Draw route legs
+		if (this.routeLegs.length > 0 && this.stationPositions.length > 0) {
+			this.drawRoute();
+		}
+
 		// Scale indicator
 		this.drawScaleBar(rect.width, rect.height);
 	}
@@ -287,6 +297,58 @@ export class SolarSystem2DRenderer {
 		ctx.fillText(info.name, sx + size + 4, sy + 3);
 	}
 
+	private drawRoute() {
+		const ctx = this.ctx;
+		const colors = ['#ff6a33', '#33ff88', '#ff33aa', '#33aaff', '#ffaa33'];
+
+		for (let i = 0; i < this.routeLegs.length; i++) {
+			const leg = this.routeLegs[i];
+			const fromX = this.stationPositions[leg.from * 3];
+			const fromY = this.stationPositions[leg.from * 3 + 1];
+			const toX = this.stationPositions[leg.to * 3];
+			const toY = this.stationPositions[leg.to * 3 + 1];
+
+			const [sx1, sy1] = this.auToScreen(fromX, fromY);
+			const [sx2, sy2] = this.auToScreen(toX, toY);
+
+			const color = colors[i % colors.length];
+
+			// Draw line
+			ctx.strokeStyle = color;
+			ctx.lineWidth = 2;
+			ctx.setLineDash([6, 4]);
+			ctx.beginPath();
+			ctx.moveTo(sx1, sy1);
+			ctx.lineTo(sx2, sy2);
+			ctx.stroke();
+			ctx.setLineDash([]);
+
+			// Arrow head
+			const angle = Math.atan2(sy2 - sy1, sx2 - sx1);
+			const arrowLen = 8;
+			ctx.fillStyle = color;
+			ctx.beginPath();
+			ctx.moveTo(sx2, sy2);
+			ctx.lineTo(
+				sx2 - arrowLen * Math.cos(angle - 0.3),
+				sy2 - arrowLen * Math.sin(angle - 0.3),
+			);
+			ctx.lineTo(
+				sx2 - arrowLen * Math.cos(angle + 0.3),
+				sy2 - arrowLen * Math.sin(angle + 0.3),
+			);
+			ctx.closePath();
+			ctx.fill();
+
+			// Leg number
+			const mx = (sx1 + sx2) / 2;
+			const my = (sy1 + sy2) / 2;
+			ctx.fillStyle = color;
+			ctx.font = 'bold 10px monospace';
+			ctx.fillText(`${i + 1}`, mx + 5, my - 5);
+		}
+	}
+
 	private drawStation(xAU: number, yAU: number, name: string) {
 		const ctx = this.ctx;
 		const [sx, sy] = this.auToScreen(xAU, yAU);