fix(parakeet-nemo): return the window cache and cap the process (nemo-0.1.1)

The gen-small EngineCore OOM (04:21 PT): our parked 3,582 MiB window cache left
no room for vLLM's runtime workspace. Seat-side fix, three controls:

- windowed path wraps every window in torch.cuda.empty_cache(), so the seat
  returns to ~2,108 MiB rest after a 12-min file instead of parking at the
  peak (measured: peak 3,028 MiB during, rest after, restarts=0);
- MEM_CAP_MIB=3840 hard set_per_process_memory_fraction: over-cap requests
  answer 503 with the seat alive (proved at cap=2000), so the failure lands
  on us, never on a neighbour;
- CUDA_GRAPHS=0: the graph decoder pins cache blocks that empty_cache must
  free (illegal-memory-access wedge when both were on first try). Cost:
  12-min file 3.0 s vs 1.2 s, short bins 35-62 ms vs 33-42 ms -- still 4-15x
  under the sherpa seat.

Measured, not computed: gen-small moved ZERO from 36,116 MiB across three
realistic requests (1,351 in / ~180 out) -- its workspace lands at engine
init; the growth window is restart-relative, matching infra-ops's observation.
WINDOW_S is now a real compose tunable. README memory section rewritten.

stacks/parakeet-nemo/compose.yaml

@@ -32,6 +32,11 @@ services:
     environment:
       - MODEL_PATH=/hf/hub/models--nvidia--parakeet-unified-en-0.6b/snapshots/${PARAKEET_NEMO_REV}/parakeet-unified-en-0.6b.nemo
       - WARMUP_SECONDS=${PARAKEET_NEMO_WARMUP:-1,8,60}
+      # CUDA graphs pin memory in torch's cache, which fights the empty_cache the windowed path
+      # needs to return memory to GPU 0's neighbours (illegal-memory-access wedge, 2026-10-01).
+      - CUDA_GRAPHS=${PARAKEET_NEMO_CUDA_GRAPHS:-0}
+      - MEM_CAP_MIB=${PARAKEET_NEMO_MEM_CAP_MIB:-3840}
+      - WINDOW_S=${PARAKEET_NEMO_WINDOW_S:-360}
       - LOG_LEVEL=${PARAKEET_NEMO_LOG_LEVEL:-INFO}
     volumes:
       - /tank/aimodels/huggingface:/hf:ro