feat: auto-detect zigzag-dir from port anchors

When `zigzag-dir` is `auto` (the new default), deduce it from the
endpoint port anchors using `detect-port-side`. East/west ports yield
"vertical" and north/south ports yield "horizontal". If the direction
cannot be deduced (no port anchor on either endpoint, or conflicting
directions) it falls back to "vertical", the previous default.

src/wire.typ

@@ -299,7 +299,7 @@
 /// - directed (bool): If true, the wire will be directed, meaning an arrow will be drawn at the endpoint
 /// - rotate-name (bool): If true, the name will be rotated according to the wire's slope
 /// - zigzag-ratio (auto, ratio): Position of the zigzag middle bend segment relative to the horizontal (or vertical) span, as a fraction between the two endpoints (only with style "zigzag"). Defaults to `auto`, which resolves to `50%`. Panics if combined with an explicitly set `zigzag-at`.
-/// - zigzag-dir (str): The zigzag's direction. As either "vertical" or "horizontal" (only with dstyle "zigzag")
+/// - zigzag-dir (auto, str): The zigzag's direction, as either "vertical" or "horizontal" (only with style "zigzag"). If `auto`, it is deduced from the endpoints when they are port anchors of the form `<elmt-id>-port-<port-id>` by comparing each port's position with its element's `.center` anchor: east/west-facing ports yield `"vertical"` (wire exits horizontally) and north/south-facing ports yield `"horizontal"`. If the direction cannot be deduced (no port anchor on either endpoint, or conflicting directions), it falls back to `"vertical"`.
 /// - zigzag-at (none, str, array, dictionary): Optional. Anchor-based placement of the zigzag middle bend segment (only with style "zigzag"). When set, overrides `zigzag-ratio` (which must be left at its default `auto`). The middle segment sits on the axis extracted from the given coordinate: `x` for `zigzag-dir: "vertical"`, `y` for `"horizontal"`. Accepted forms: a raw CeTZ anchor name string (e.g. `"elmt.center"` or `"elmt-port-a"`); any native CeTZ coordinate (tuple, dict such as `(rel: (dx, dy), to: anchor)`); or the ergonomic scalar-offset form `(rel: <length>, to: <coord>)`, which is rewritten to a `(dx, 0)` offset for `"vertical"` and `(0, dy)` for `"horizontal"`. See #examples.zigzag-at
 /// - dodge-y (number): Y position to dodge the wire to (only with style "dodge")
 /// - dodge-sides (array): The start and end sides (going out of the connected element) of the wire (only with style "dodge")
@@ -323,7 +323,7 @@
   directed: false,
   rotate-name: true,
   zigzag-ratio: auto,
-  zigzag-dir: "vertical",
+  zigzag-dir: auto,
   zigzag-at: none,
   dodge-y: 0,
   dodge-sides: ("east", "west"),
@@ -368,11 +368,25 @@
     (points, anchors) = get-direct-wire(pts)
     
   } else if style == "zigzag" {
+    let zz-dir = zigzag-dir
+    if zz-dir == auto {
+      let side-start = detect-port-side(pts.first(), ctx)
+      let side-end = detect-port-side(pts.last(), ctx)
+      let dir-from-side(s) = if s == none { none } else if s == "east" or s == "west" { "vertical" } else { "horizontal" }
+      let d-start = dir-from-side(side-start)
+      let d-end = dir-from-side(side-end)
+      // Fall back to "vertical" (the previous default) when the direction
+      // cannot be deduced (no port anchors, or conflicting endpoints).
+      if d-start != none and d-end != none and d-start != d-end { zz-dir = "vertical" }
+      else if d-start != none { zz-dir = d-start }
+      else if d-end != none { zz-dir = d-end }
+      else { zz-dir = "vertical" }
+    }
     (points, anchors) = get-zigzag-wire(
       pts,
       zigzag-ratio-effective,
-      zigzag-dir,
-      at: normalize-zigzag-at(zigzag-at, zigzag-dir),
+      zz-dir,
+      at: normalize-zigzag-at(zigzag-at, zz-dir),
     )
     
   } else if style == "dodge" {