v0.4.63: SSO row alignment, themed checkbox, dropdown affordance

Three UI nits the operator caught on v0.4.62, plus the queued PXE-theme
research note for the next release.

- SSO header grid is now a 4-column form-row matching the Administrator
  account card column-for-column (display name / logo URL / metadata
  source / metadata URL). Switching to XML mode collapses column 4 and
  drops the multi-line textarea on its own full-width row below.
- Native form chrome (checkboxes, scroll bars) follows the active
  OpenPXE theme via CSS `color-scheme`; the inline meta tag was forcing
  dark form controls in light mode, which is why the "Enable single
  sign-on" checkbox rendered as an opaque black square against the
  light panel.
- Checkbox itself is now custom-styled (16x16 rounded square, accent
  fill + tick on :checked) so the chrome reads identically across both
  palettes and browsers, not just on whichever WebKit happens to honor
  `accent-color`.
- <select> dropdowns get a hand-drawn chevron via background-image SVG;
  with `-webkit-appearance: none` the native arrow had disappeared,
  making "Metadata source" look squished next to the inputs beside it.
- Update credentials + Save SSO settings buttons get explicit top
  margins so they sit clearly under their input rows instead of butting
  against the field beneath.
- `docs/queued/ipxe-pxe-menu-theme-research.md` captures findings on
  how iVentoy paints its boot menu (iPXE `console --picture` with
  baked-in per-resolution PNGs, no EDID auto-detect) and the
  recommended Rust architecture for the follow-up release.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

Cargo.lock

@@ -1140,7 +1140,7 @@ checksum = "384b8ab6d37215f3c5301a95a4accb5d64aa607f1fcb26a11b5303878451b4fe"
 
 [[package]]
 name = "openpxe"
-version = "0.4.62"
+version = "0.4.63"
 dependencies = [
  "anyhow",
  "axum",
@@ -1162,7 +1162,7 @@ dependencies = [
 
 [[package]]
 name = "openpxe-core"
-version = "0.4.62"
+version = "0.4.63"
 dependencies = [
  "anyhow",
  "bcrypt",
@@ -1181,7 +1181,7 @@ dependencies = [
 
 [[package]]
 name = "openpxe-dhcp-proxy"
-version = "0.4.62"
+version = "0.4.63"
 dependencies = [
  "anyhow",
  "bytes",
@@ -1195,7 +1195,7 @@ dependencies = [
 
 [[package]]
 name = "openpxe-http-api"
-version = "0.4.62"
+version = "0.4.63"
 dependencies = [
  "anyhow",
  "axum",
@@ -1226,7 +1226,7 @@ dependencies = [
 
 [[package]]
 name = "openpxe-ipxe-assets"
-version = "0.4.62"
+version = "0.4.63"
 dependencies = [
  "openpxe-core",
  "rust-embed",
@@ -1236,7 +1236,7 @@ dependencies = [
 
 [[package]]
 name = "openpxe-iso-store"
-version = "0.4.62"
+version = "0.4.63"
 dependencies = [
  "anyhow",
  "bcrypt",
@@ -1260,7 +1260,7 @@ dependencies = [
 
 [[package]]
 name = "openpxe-tftp"
-version = "0.4.62"
+version = "0.4.63"
 dependencies = [
  "anyhow",
  "bytes",
@@ -1274,7 +1274,7 @@ dependencies = [
 
 [[package]]
 name = "openpxe-webui"
-version = "0.4.62"
+version = "0.4.63"
 
 [[package]]
 name = "parking_lot"