host: relate/unrelate keep both lists in sync (add to current list, never blank the picker)

Two reported bugs on the edit page's relation editor:
 1. relating a candidate didn't add it to the current-relations list (the AJAX
    relate just deleted the candidate row; the relation only showed after a reload);
 2. removing a relation could blank the relate picker.

Fix (lib/host/blog.sx): both the candidate's relate form and a current relation's
remove form now target #rel-editor-<kind> with sx-swap=outerHTML, and the
relate/unrelate handlers return the re-rendered editor for that kind (current list +
a fresh picker). So one swap keeps BOTH lists in sync: the related post moves into
the current list and out of the (re-loaded) candidate pool; removing moves it back.
Gated on the SX-Target header, so a plain boosted form / no-JS POST (the is-a-tag
toggle) still redirects + re-renders #content.

Engine fix (web/orchestration.sx): handle-html-response's non-select branch called
post-swap on the OLD target, which an outerHTML swap has already REPLACED — so the
swapped-in content's triggers (here the re-rendered picker's "load") never bound and
the picker stayed empty. post-swap the swap result (the new node), mirroring the
sx-select branch. Recompiled orchestration.sxbc for the content-addressed client.

Tests:
 - web/tests/test-relate-picker.sx: relating re-syncs the editor (post in current
   list + picker re-loads); removing does likewise — both fail without the engine fix.
 - lib/host/tests/blog.sx: relate/unrelate return the re-rendered editor fragment
   (200, #rel-editor + picker), forms wire to #rel-editor-KIND/outerHTML, plain
   boosted POST still 303.
 - relate-picker.spec.js: the full in-page flow (relate adds to list, remove keeps
   the picker, no reload) + persistence.

Verified: host conformance 277/277, web engine suite 8/8, run-picker-check 3/3,
run-spa-check 3/3.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

shared/static/wasm/sx/orchestration.sx

@@ -467,11 +467,19 @@
                     use-transition
                     (fn
                       ()
-                      (swap-dom-nodes
-                        target
-                        (children-to-fragment container)
-                        swap-style)
-                      (post-swap target))))))))))
+                      ;; post-swap the NEW node, not the old target — an outerHTML
+                      ;; swap REPLACES target, so processing target would re-bind a
+                      ;; detached node and leave the swapped-in content's triggers
+                      ;; (e.g. a re-rendered picker's "load") unbound. Mirrors the
+                      ;; sx-select branch above. For innerHTML swap-root falls back
+                      ;; to target (still in the document).
+                      (let
+                        ((swap-root
+                          (swap-dom-nodes
+                            target
+                            (children-to-fragment container)
+                            swap-style)))
+                        (post-swap (or swap-root target))))))))))))
     (define
       handle-retry
       :effects (mutation io)