feat(steps): draw all arms of conditional navigations as separate edges

Adds multi-arm navigation support: when a destination is produced by a conditional, every arm is now drawn as its own edge. Introduces helpers (hrefArms, destinationsForHref) and updates framework resolvers and edge creation to emit multiple navigates edges (via alsoTargets) instead of a single one. Also introduces per-app rooted route tables to avoid cross-app crossings, and updates various resolvers (React Router, TanStack Router, Vue Router, SvelteKit, Vue, and SvelteKit’s linker) and the UI to reflect multiple possible destinations. Tests and docs updated to reflect the new behavior, ensuring the Screens tab shows all possible navigation paths from conditional destinations. This makes navigation visualization more accurate for forked destinations.

__tests__/expo-router.test.ts

@@ -140,11 +140,30 @@ describe('expo-router: readHrefArgument', () => {
     const r = read(src, 'navigate');
     expect(r?.path).toBe('/sheets/create-detection-item');
     expect(r?.display).toBe('/sheets/create-detection-item?folderId=${…}');
-    expect(r?.alternate?.path).toBe('/sheets/create-detection-item');
+    expect(r?.alternates?.map((a) => a.path)).toEqual(['/sheets/create-detection-item']);
   });
 
-  it('returns null when one arm of a conditional is not a literal', () => {
-    expect(read("router.push(ready ? '/home' : fallback)")).toBeNull();
+  it('reads the literal arm when the other is not one — a place the code demonstrably goes', () => {
+    // Both arms readable is a fork, and `pageForHref` resolves it only when
+    // they name the same route. One arm readable is not a fork: `/home` is
+    // somewhere this call goes, and reporting it is not a guess. Dropping it
+    // cost every react-router app its post-login transition, which is written
+    // `const redirect = search ? search.split('=')[1] : '/'`.
+    const r = read("router.push(ready ? '/home' : fallback)");
+    expect(r?.path).toBe('/home');
+    expect(r?.alternate).toBeUndefined();
+    expect(read("router.push(ready ? fallback : '/home')")?.path).toBe('/home');
+    // Neither arm readable is still nothing.
+    expect(read('router.push(ready ? a : b)')).toBeNull();
+  });
+
+  it('pairs the arms of a NESTED conditional, and keeps all three', () => {
+    // Taking the first `:` split this between `keyword` and '/page', reading
+    // '/page' — a real path, from the wrong arm of the wrong conditional. Paired
+    // properly it is a paginator that goes to one of three places, and the
+    // picture draws all three rather than none.
+    const r = read("router.push(!isAdmin ? keyword ? '/search' : '/page' : '/admin')");
+    expect([r?.path, ...(r?.alternates ?? []).map((a) => a.path)]).toEqual(['/search', '/page', '/admin']);
   });
 
   it('reads only the first argument', () => {
@@ -190,7 +209,7 @@ describe('expo-router: readHrefViaLocal', () => {
       '  }\n}';
     const r = viaLocal(src);
     expect(r?.path).toBe('/barcode-scan');
-    expect(r?.alternate?.path).toBe('/barcode-scan');
+    expect(r?.alternates?.map((a) => a.path)).toEqual(['/barcode-scan']);
   });
 
   it('reads a typed declaration and an Href object initializer', () => {
@@ -369,9 +388,14 @@ describe('expo-router: resolve', () => {
     expect(expoRouterResolver.resolve(ref('list.push', 12, 32), context)?.targetNodeId).toBe(routes[2]!.id);
   });
 
-  it('binds a conditional whose arms name the same screen, refuses one that forks', () => {
-    expect(expoRouterResolver.resolve(ref('router.push', 14, 33), context)?.targetNodeId).toBe(routes[2]!.id);
-    expect(expoRouterResolver.resolve(ref('router.push', 13, 27), context)).toBeNull();
+  it('binds a conditional whose arms name the same screen, and draws BOTH when they fork', () => {
+    const same = expoRouterResolver.resolve(ref('router.push', 14, 33), context);
+    expect(same?.targetNodeId).toBe(routes[2]!.id);
+    expect(same?.alsoTargets).toBeUndefined();
+    // A fork reaches both screens, and each becomes an edge of its own.
+    const forked = expoRouterResolver.resolve(ref('router.push', 13, 27), context);
+    expect(forked).not.toBeNull();
+    expect([forked!.targetNodeId, ...(forked!.alsoTargets ?? []).map((t) => t.targetNodeId)]).toHaveLength(2);
   });
 
   it('ignores refs that are not calls or not JS/TS', () => {