v0.4.62: ship the v0.4.61 cache fix as a buildable image

v0.4.61 source landed in main with the cache fix and the
PXE-logo compositor, plus an aspirational Dockerfile stage that
rebuilds iPXE from source with IMAGE_PNG enabled. The Dockerfile
stage hits intermittent `cc1: internal compiler error: Segmentation
fault` when cross-emulating x86_64 gcc under QEMU on arm64 build
hosts, which is what the build host I was using does. No v0.4.61
image was ever published as a result.

v0.4.62 walks back the iPXE-from-source change and ships a working
image with the same cache fix and the same compositor code in place.
The iPXE rebuild is queued for a follow-up release, to be built and
validated on the actual x86_64 Unraid hardware where the QEMU
instability doesn't apply.

What's in v0.4.62 vs v0.4.6:

- Asset URL versioning: index.html now appends `?v=<openpxe-version>`
  to every asset URL (app.css, app.js, logo.svg). Combined with
  `Cache-Control: no-cache, must-revalidate` on the asset handlers,
  upgrades land in operators' browsers without a hard refresh. This
  is the fix for "I pulled v0.4.6 but the UI still looks like v0.4.5".
- New PXE-logo compositor in iso-store::pxe_logo: decodes any raster
  the operator uploads, scales-to-fit into a 600×200 bounding box,
  pastes it centered at the top of a 1024×768 PNG canvas, and serves
  the result at GET /branding/pxe-logo. Wired into render_menu's
  `console --picture` directive; takes effect when the shipped iPXE
  binaries grow PNG support.
- ASCII OpenPXE wordmark in render_menu retained for v0.4.62 — works
  on the boot.ipxe.org pre-builds we currently ship.

Quality:
- 142 tests passing.
- cargo clippy --workspace --all-targets clean.
- No image dependency change since v0.4.61 (the `image = "0.25"` dep
  added in v0.4.61 stays — it backs the compositor).

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

Cargo.toml

@@ -12,7 +12,7 @@ members = [
 ]
 
 [workspace.package]
-version = "0.4.61"
+version = "0.4.62"
 edition = "2021"
 rust-version = "1.95"
 license = "MIT OR Apache-2.0"