Add multi-route comparison with Yen's k-shortest-paths algorithm

- Yen's algorithm in Rust: finds up to 3 distinct shortest routes by
  iteratively deviating from previously found paths with node exclusions
- Routes are deduplicated by station sequence (same stations = same route
  even if timing differs slightly)
- Dijkstra refactored to support node exclusion sets for Yen's spur paths
- WASM API returns JSON array of RouteResult (was single object)
- Frontend routing store holds multiple routes with selectedRouteIndex
- Route tabs: "Fastest", "Alternative 1", "Alternative 2" with distinct
  colors (orange, blue, purple), click to switch and resample trajectory
- Compact route planner layout: 2-column From/To, shorter window buttons
- Tested: Earth L1 → Jupiter L1 finds 2-leg relay via Mercury L1 (6.9mo)

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

crates/mass-driver-wasm/src/api.rs

@@ -213,17 +213,19 @@ pub fn compute_route(
         },
     );
 
-    // Find optimal route
-    let route = router::find_optimal_route(
+    // Find up to 3 shortest routes using Yen's algorithm
+    let routes = router::find_k_shortest_routes(
         &matrix,
         from_station,
         to_station,
         0,
         week_window.saturating_sub(1),
+        3,
     );
 
-    match route {
-        Some(r) => serde_json::to_string(&r).unwrap_or_default(),
-        None => String::new(),
+    if routes.is_empty() {
+        String::new()
+    } else {
+        serde_json::to_string(&routes).unwrap_or_default()
     }
 }