v0.5.9: El Torito boot detection + retroactive re-introspect; static SSO login button

Storage / boot detection
- Add El Torito boot-catalog detection to ISO introspection. This is the
  authoritative "can this boot at all?" signal: any ISO with a boot catalog
  (BSDs, ESXi, firmware tools, custom spins) is bootable via iPXE sanboot;
  a data/appliance ISO (e.g. a VMware vCenter bundle) has none and is
  honestly flagged. Replaces the crude ">1.5 GB ⇒ unbootable" size guess.
- Re-introspect stale LOCAL ISOs on startup via an introspection-revision
  gate (INTROSPECT_REV). ISOs uploaded by an older binary carried a frozen
  family/boot profile — most visibly a Windows 11 ISO tagged Unknown before
  the UDF/UTF-16 detection landed, which then showed "won't boot" forever.
  An upgrade now re-probes and fixes them in place; no delete-and-re-upload.
- WebUI bootability() keys off family / kernel / el_torito / remote-source
  instead of the size heuristic; dashboard family counts now bucket
  Windows / Linux / other honestly instead of lumping everything non-Windows
  under "Linux".

SSO login button
- The "Sign in with …" button keyed off the auth-gated /api/sso, which 401s
  pre-auth — so the button only survived on a stale in-memory config and
  vanished instance-wide on any fresh login-page load. Ship a minimal,
  non-sensitive SSO descriptor (enabled + idp_name + idp_logo_url, no
  metadata/entity-ID) on the public /api/me; the login card reads that.
  The button is now static whenever SSO is usable.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

Cargo.lock

@@ -2669,7 +2669,7 @@ checksum = "c08d65885ee38876c4f86fa503fb49d7b507c2b62552df7c70b2fce627e06381"
 
 [[package]]
 name = "openpxe"
-version = "0.5.8"
+version = "0.5.9"
 dependencies = [
  "anyhow",
  "axum",
@@ -2691,7 +2691,7 @@ dependencies = [
 
 [[package]]
 name = "openpxe-core"
-version = "0.5.8"
+version = "0.5.9"
 dependencies = [
  "anyhow",
  "base64",
@@ -2718,7 +2718,7 @@ dependencies = [
 
 [[package]]
 name = "openpxe-dhcp-proxy"
-version = "0.5.8"
+version = "0.5.9"
 dependencies = [
  "anyhow",
  "bytes",
@@ -2732,7 +2732,7 @@ dependencies = [
 
 [[package]]
 name = "openpxe-http-api"
-version = "0.5.8"
+version = "0.5.9"
 dependencies = [
  "anyhow",
  "axum",
@@ -2768,7 +2768,7 @@ dependencies = [
 
 [[package]]
 name = "openpxe-ipxe-assets"
-version = "0.5.8"
+version = "0.5.9"
 dependencies = [
  "openpxe-core",
  "rust-embed",
@@ -2778,7 +2778,7 @@ dependencies = [
 
 [[package]]
 name = "openpxe-iso-store"
-version = "0.5.8"
+version = "0.5.9"
 dependencies = [
  "anyhow",
  "bcrypt",
@@ -2807,7 +2807,7 @@ dependencies = [
 
 [[package]]
 name = "openpxe-tftp"
-version = "0.5.8"
+version = "0.5.9"
 dependencies = [
  "anyhow",
  "bytes",
@@ -2821,7 +2821,7 @@ dependencies = [
 
 [[package]]
 name = "openpxe-webui"
-version = "0.5.8"
+version = "0.5.9"
 
 [[package]]
 name = "p256"