v0.6.0: bootable-ISO polish + close the 0.5.x chapter

Builds on v0.5.9's El Torito detection to make the boot menu honest and
clean, and confirms generic El Torito ISOs (ESXi/VMvisor installers, BSDs,
firmware tools) boot via iPXE sanboot with no special-casing:

- generate_boot_entries: an Unknown-family ISO now produces a sanboot entry
  only when it's actually bootable — it carries an El Torito catalog, OR it's
  a remote-share ISO we couldn't introspect (rev 0, assumed bootable). A
  locally-introspected ISO with no boot catalog (a data/appliance image like
  a VMware vCenter Server Appliance bundle) yields NO entry, so it stays out
  of the iPXE menu instead of offering a pick that always fails. ESXi
  installers (Unknown family + El Torito) surface under the installer menu
  and sanboot the raw ISO — backed by HTTP range reads, so size is moot.
- Dropped the stale "(SAN boot — may fail for >1GiB ISOs)" disclaimer and
  refreshed the SanBootIso doc: sanboot is the primary path for Windows and
  any El Torito image, and HTTP range reads remove the size limit.
- WebUI: renamed the dashboard panel "Images that won't boot with current
  settings" -> "Non-bootable images" (there's no setting that would make a
  data/appliance ISO boot).
- Tests: el_torito catalog detection + boot-entry generation across the
  ESXi / VCSA / remote-share cases.

Full v0.5.0->v0.5.9 compatibility sweep: clippy clean; entire workspace test
suite green (core 96, http-api 31+68, iso-store 61, dhcp 1, tftp 6, bin 2);
app.js syntax-checked.

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

crates/iso-store/src/entry.rs

@@ -25,9 +25,11 @@ pub enum BootKind {
         wimboot_url: String,
         files: Vec<(String, String)>,
     },
-    /// Last-resort: SAN-boot the ISO as an emulated CD. Only works for small
-    /// ISOs (<~1 GiB) and older distros. Kept for completeness, not the
-    /// default.
+    /// SAN-boot the raw ISO as an emulated CD (iPXE `sanboot`). The emulated
+    /// CD is backed by on-demand HTTP range reads, so ISO size is *not* a
+    /// constraint — this is the primary path for Windows (v0.5.8) and for any
+    /// El Torito-bootable image we don't special-case: ESXi/VMvisor
+    /// installers, BSDs, firmware/diagnostic tools, custom spins (v0.6.0).
     SanBootIso { iso_url: String },
 }