[fabricio3g]

Backend correctness (verified against sd-cli master-820-de298c2):

• Emit --model-args instead of the four --chroma-* / --qwen-image-zero-cond-t flags, which current sd.cpp no longer accepts. The old spelling is kept for binaries that still advertise it, chosen per-run from a capability probe.
• Fix the SD3.5 pack's CLIP-G download, which 400ed because 'clipG' is not a model directory key. resolveModelDirectoryKey maps it to clip/.
• Classify "unknown argument" failures instead of showing a generic error. runCli keeps the first error line before the usage dump evicts it.
• Detect backend folders built for another OS (sd-cli.exe on Linux), which satisfied backendHasBinaries but could never run.
• Extract parseCliHelp into a pure shared module with an exact-match hasHelpFlag, plus a server-side capability cache invalidated on backend switch. Refresh the checked-in help dumps and use them as a test fixture.

Settings and setup UI:

• Add an About panel with app version, build date, and runtime details, injected at build time from package.json.
• Drop the pinned "recommended runtime" tag; the Installation panel now recommends the newest release and lists every published binary, labelled with OS and accelerator.
• Show "None installed" rather than a phantom version when the stored backend is not on disk.
• Restyle the setup wizard, add a way to skip the runtime download, and simplify the welcome and model steps.
• Add an SD 1.5 starter pack (smallest) sourced from the sd.cpp docs.
• Share one empty-state hero across the Image, Edit, and Video stages.
• Keep the quantization output filename in sync with the target format.

Tests: 104 -> 137.