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]>

crates/iso-store/src/nfs_share.rs

@@ -57,7 +57,7 @@
 //! UI to ask for. (If a future server needs Kerberos or non-default
 //! uid mapping we can add those, but for ISO read access nobody does.)
 
-use crate::introspect::{DistroFamily, IntrospectionReport};
+use crate::introspect::IntrospectionReport;
 use crate::store::{generate_boot_entries_for, slugify_str, IsoSource, IsoStore};
 use bytes::Bytes;
 use nfs3_client::tokio::TokioConnector;
@@ -399,13 +399,7 @@ impl NfsShareManager {
             // Same approach as SMB: no real introspection over the
             // network in v0.4.67. The boot-entry generator falls back
             // to filename-based sanboot detection.
-            let report = IntrospectionReport {
-                family: DistroFamily::Unknown,
-                volume_label: None,
-                kernel_path: None,
-                initrd_paths: Vec::new(),
-                has_boot_wim: false,
-            };
+            let report = IntrospectionReport::default();
             let boot_entries = generate_boot_entries_for(&iso_id, &entry.filename, &report);
             let source = IsoSource::Nfs {
                 share_id: share.id.clone(),