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/webui/src/app.js

@@ -365,7 +365,7 @@
       const settings = status.settings;
       const problems = isos.map(i => ({i, b: bootability(i, settings)})).filter(x => !x.b.ok);
       const problemsBlock = problems.length ? el('div', {class:'card'}, [
-        el('header', {}, [el('h2', {}, 'Images that won\'t boot with current settings')]),
+        el('header', {}, [el('h2', {}, 'Non-bootable images')]),
         el('div', {class:'body'},
           problems.map(({i, b}) => el('div', {class:'row-warn'},
             '⚠ ' + i.filename + ' — ' + b.reason)))