fix(admin): stop cropping the layout preview images in image_select

AksImageSelectField pinned every preview to a 60x60 box with
object-fit:cover, but these are wide layout strips: header layouts are
597x57 (10.47:1), the footer template is 800x190 (4.21:1) and the slide
align set is 200x101. A 10:1 strip inside a square crop keeps ~6% of its
width, so the layout it is supposed to illustrate is unrecognisable.

Constrain the width instead and let the height follow, which is what the
reference theme's CSF image_select does (max-width:100%; height:auto).
Each field now declares the width that suits its images, and an option
may still override it: header 200, footer 240, slide align 160, mobile
header 120.

Only presentation changed. No image files and no stored values moved,
so existing settings are unaffected.

tools/admin-contract-report.json

@@ -1,5 +1,5 @@
 {
-    "generated_at": "2026-11-01T03:45:46+00:00",
+    "generated_at": "2026-11-01T04:11:06+00:00",
     "errors": [],
     "warnings": [
         "customPage tools-update section 'tools/update' not in PHP schema (ok if pure operational page)",
@@ -258,7 +258,7 @@
         "entry": true,
         "missing_chunks": [],
         "chunks": [
-            "SchemaPage.BM05qq7c.js",
+            "SchemaPage.YNr16Fc9.js",
             "vendor-vue.CibbKclz.js",
             "FaIcon.DB-L86Cm.js",
             "useCollapsibleItems.B7EjDmsr.js",
@@ -276,8 +276,8 @@
             "FloatingButtonsSettings.DYWR59AW.js",
             "PageHeader.UHsfBDVL.js",
             "FooterTabbarSettings.D8ujMgd9.js",
-            "PostPageSettings.Bhei4Dk4.js",
-            "CommentSettings.Ct-HES9S.js",
+            "PostPageSettings.D8BXJ07f.js",
+            "CommentSettings.1Il-GVqw.js",
             "PermissionsCapabilities.DXXFzINq.js",
             "CmsCredits.DESOnIkP.js",
             "ThemeInfoPage.D5AogccB.js",
@@ -287,7 +287,7 @@
             "UsersLevel.B-jXEukF.js",
             "UsersBadge.DVCEC3QE.js",
             "UsersWechatTemplate.DHoNsqm_.js",
-            "UsersTicket.DcwmQE5D.js",
+            "UsersTicket.D5BTFq6U.js",
             "ToolsImportExport.C-XhCKwl.js",
             "ToolsHealth.DNZ1YaWo.js",
             "ToolsUpdate.38p6GYou.js"