v0.3.0 — llama.cpp backend selection + AMD GPU support on Linux

New

• llama.cpp backend selection — install the build matching the machine's GPU: CUDA, ROCm/HIP, Vulkan or CPU. auto decides on its own (NVIDIA → CUDA, AMD/Intel → Vulkan, Apple → Metal), and the installer downloads the matching official asset instead of always the CUDA one; CUDA also pulls the matching cudart runtime.
• AMD/Intel GPUs on Linux — Radeon and Intel cards are now detected in the hardware check and in the live monitor, read from sysfs amdgpu counters. A Radeon machine on Linux used to be reported as having no GPU.

Fixes

• One-click install on NVIDIA machines pulled the CPU build — backend selection reads a vendor field that the nvidia-smi path never filled in, so every NVIDIA machine looked GPU-less and got the CPU package.
• The Windows installer was broken before that too — it asked for releases/latest and matched a hard-coded bin-win-cuda-cu12 asset name, while upstream now ships cuda-12.4 / rocm-10.0 / vulkan / cpu assets and its newest release carries no platform binaries at all.
• Saving a target no longer duplicates it (#1) — the Settings form always started blank, so every save appended a new entry. Targets now match by id first, then by host/port/user/name, and an existing one can be loaded back into the form.
• Failed install steps are reported instead of being silently dropped.

Full Changelog: v0.2.0...v0.3.0