fix: preserve edge connection points in YAML export/import (#208)

YAML round-trip dropped every edge's handles: export never wrote them
and import hardcoded sourceHandle='bottom'/targetHandle='top-t'. After
import all connections collapsed onto slot 0 ("converge at a single
point"). Per-side handle counts were dropped too, so the extra bottom
slots did not even exist to attach to.

- yaml types: add sourceHandle/targetHandle to connections and
  top/bottom/left/rightHandles to nodes
- export: write each edge's real handles + per-side counts (only above
  the side default); orient parent-edge handles parent->child
- import: restore handle counts onto node data and use the stored
  handles, falling back to the legacy defaults for pre-existing YAML

Positions remain dagre-managed (unchanged); this restores connection
points only.

ha-relevant: yes

frontend/src/utils/importYaml.ts

@@ -73,6 +73,12 @@ export function parseYamlToCanvas(
       ...(yn.ram ? { ram_gb: yn.ram } : {}),
       ...(yn.disk ? { disk_gb: yn.disk } : {}),
       ...(hasHardware ? { show_hardware: true } : {}),
+      // Restore custom connection-point counts so the edges below attach to the
+      // slots they were exported on instead of collapsing onto slot 0.
+      ...(yn.topHandles ? { top_handles: yn.topHandles } : {}),
+      ...(yn.bottomHandles ? { bottom_handles: yn.bottomHandles } : {}),
+      ...(yn.leftHandles ? { left_handles: yn.leftHandles } : {}),
+      ...(yn.rightHandles ? { right_handles: yn.rightHandles } : {}),
     }
 
     newNodes.push({
@@ -104,12 +110,14 @@ export function parseYamlToCanvas(
     if (edgePairs.has(key) || edgePairs.has(reverseKey)) return
     edgePairs.add(key)
     const edgeType = conn.linkType ?? 'ethernet'
+    // Prefer the exported connection points; fall back to the legacy defaults for
+    // YAML written before handles were persisted.
     newEdges.push({
       id: generateUUID(),
       source: sourceId,
       target: targetId,
-      sourceHandle,
-      targetHandle,
+      sourceHandle: conn.sourceHandle ?? sourceHandle,
+      targetHandle: conn.targetHandle ?? targetHandle,
       type: edgeType,
       data: {
         type: edgeType,