manager (record_vram_delta): record the FULL footprint after a load — including
offloaded loads (no longer skipped) — so the next load skips the OOM→move-to-RAM
retry dance:
  * measured_vram_gb      — GPU VRAM delta + reserve (GPU portion; eviction uses it)
  * measured_ram_gb       — host-RAM delta (the CPU-offloaded layers)   [new]
  * measured_n_gpu_layers — the layer split llama.cpp settled on         [new]
  total need = vram + ram. All gated by force_vram_update (else only when
  used_vram_gb unset). New _learned_n_gpu_layers(): when n_gpu_layers is auto/-1,
  reuse the learned split so a reload jumps straight to the config that fit. Both
  load sites snapshot host RAM and read the backend's settled n_gpu_layers.

frontproxy:
  * graceful streaming proxy: when an engine dies mid-stream (e.g. a CUDA
    ggml_abort SIGABRT on a VRAM-OOM decode), end the relayed stream cleanly
    instead of throwing an unhandled ASGI exception (noisy traceback).
  * task actions (cancel/interrupt/pause/resume/restart/DELETE) now route to the
    engine that OWNS the task — fan out to every live engine (each validates the
    same session cookie), first success wins — fixing 'Task not found' for tasks on
    a non-primary engine; front-only synthetic ids handled locally.

Bump version to 0.1.7.