…rage) (#75)

PR #72 added the --fit-print-plan flag to llama-fit-params without test
coverage. This adds a tools/fit-params/tests.sh (pattern lifted from
tools/gguf-split/tests.sh) that downloads a small Qwen3-0.6B GGUF and
verifies six invariants:

1. success-path emits single-line JSON
2. schema has per_device_bytes / n_devices / total_bytes with correct types
3. len(per_device_bytes) == n_devices
4. total_bytes == sum(per_device_bytes)
5. on CPU-only builds (n_devices==0): plan is empty, total is 0
6. fit-failure (nonexistent model) emits the documented "error":"fit_failed"
   JSON marker on stdout (not garbage) so subprocess callers can
   distinguish fit-failure from parse-failure

Run with: tools/fit-params/tests.sh path/to/build/bin

Verified locally on CPU-only build: ALL fit-params --fit-print-plan
smoke tests PASSED.

…#66 step 2 prep) (#72)

* feat(fit-params): --fit-print-plan emits per-device byte plan as JSON (#66 step 2 prep)

The router's per-GPU admit decision (#66) needs the per-device byte
demand for a candidate model BEFORE spawning the child subprocess.
PR #69 added the underlying `out_bytes_per_device` output to
`common_fit_params`; this PR exposes it via the existing
`tools/fit-params` CLI as a subprocess-friendly JSON output.

* New CLI flag `--fit-print-plan` (env `LLAMA_ARG_FIT_PRINT_PLAN`).
* On success, prints a single-line JSON object on stdout:
    {"per_device_bytes":[N0,N1,...],"n_devices":K,"total_bytes":T}
  plan[i] = i-th GPU/accel device, same order as tensor_split; CPU
  host memory NOT included. Empty plan for CPU-only builds.
* On fit failure, emits an explicit JSON failure marker and exits 1:
    {"error":"fit_failed","status":N}
* common/fit.cpp: populate `out_bytes_per_device` at the three early-
  return paths (the impl had three 'no changes needed' fast-paths that
  bypassed the main return point where PR #69 wrote the plan). Doc
  string in common/fit.h corrected — plan covers GPU devices only.

Designed to be subprocessed from `server_models::compute_admit_plan(name)`
(#66 step 2 — out-of-process approach per the architectural call on
issue #66 / task ggml-org#123). The router parses this JSON, tracks
`reserved[d]` for in-flight LOADING models, admits candidates against
`live_cudaMemGetInfo(d) - reserved[d]`. Mutually exclusive with the
existing `--fit-print` mode; if both set, `--fit-print-plan` wins.

Local CPU build verified: `--help` renders the new flag, empty plan
returned for CPU-only build as expected. GPU verification deferred to
snoop-kube's canary-cycle.

* test(fit-params): smoke for --fit-print-plan JSON output (PR #72 coverage) (#75)

PR #72 added the --fit-print-plan flag to llama-fit-params without test
coverage. This adds a tools/fit-params/tests.sh (pattern lifted from
tools/gguf-split/tests.sh) that downloads a small Qwen3-0.6B GGUF and
verifies six invariants:

1. success-path emits single-line JSON
2. schema has per_device_bytes / n_devices / total_bytes with correct types
3. len(per_device_bytes) == n_devices
4. total_bytes == sum(per_device_bytes)
5. on CPU-only builds (n_devices==0): plan is empty, total is 0
6. fit-failure (nonexistent model) emits the documented "error":"fit_failed"
   JSON marker on stdout (not garbage) so subprocess callers can
   distinguish fit-failure from parse-failure

Run with: tools/fit-params/tests.sh path/to/build/bin

Verified locally on CPU-only build: ALL fit-params --fit-print-plan
smoke tests PASSED.