Asset picker: attach/detach/reorder UI, read-only view, autosave fix

Replaces nodes#edit's old Images section -- a hidden panel dumping
every image asset in the system unfiltered (#image_browser) plus a
raw drag-and-drop box (#image_box) -- with a small search-and-click
picker built on the endpoint from the last two commits. Attaching
posts immediately and appends the new thumbnail via a cloned
<template> -- icons only render correctly through the Rails helper
server-side, so the template holds real, pre-rendered markup for JS
to clone rather than duplicating raw SVG in a JS string. Reordering is
jQuery UI sortable on the small attached list only, with a dedicated
drag handle rather than the whole thumbnail.

Two bugs caught while click-testing, fixed here rather than shipped
and patched after: the search panel never closed after attaching an
image, since the success handler re-triggered focus to keep it open
for attaching several in a row -- which meant it just re-populated
itself forever instead of signaling "done." Fixed to close explicitly;
a click-outside-closes handler was added alongside it, matching the
affordance the top-bar search already has.

A real, independent, pre-existing data bug surfaced during the same
testing: Node#autosave!'s first-time-creation branch never carried
related assets forward from whatever page was previously current --
attach an image, let autosave fire once, and it silently landed on a
fresh, assetless Page row. Long-dormant, not introduced by this work,
just finally exercised by something that made it visible. Fixed inside
the `unless self.autosave` guard specifically -- running this on every
call, not just creation, would overwrite anything attached directly to
an existing autosave in between, a worse bug than the one being fixed.

nodes#show gains a read-only Images section, rendered only when a page
actually has attached images, so an attachment can be confirmed
present without entering the edit/lock cycle -- useful on its own, and
specifically useful the next time an asset bug needs investigating.
Its thumbnail CSS is shared with the edit view's picker via a class
(.thumbnail_list) rather than duplicated under a second name.

1 files changed, 2 insertions, 0 deletions

diff --git a/test/controllers/related_assets_controller_test.rb b/test/controllers/related_assets_controller_test.rb
index 7f6d487..9d20cbb 100644
--- a/test/controllers/related_assets_controller_test.rb
+++ b/test/controllers/related_assets_controller_test.rb
@@ -44,6 +44,8 @@ class RelatedAssetsControllerTest < ActionController::TestCase
 
     assert_response :success
     assert_includes node.draft.reload.related_assets.map(&:asset_id), asset.id
+    json = JSON.parse(response.body)
+    assert json["url"].present?
   end
 
   test "create does not duplicate an already-attached asset" do