PY-PORT-2e: port llama_fit_verdict.py to aprender-ci-tools llama-fit-verdict (C301) #4799

Sub-ticket of #4741 (PY-PORT-2, C301: the build is Rust only; Python stays only as an external oracle).

Port scripts/lib/llama_fit_verdict.py (120 lines, stdlib json/re/struct) to an aprender-ci-tools llama-fit-verdict subcommand.

Acceptance:

• Same argv (tool_found pin rc free_mib version_file stdout_file model_path), byte-identical stdout (Python json.dumps key order and escaping) and the same exit status as the .py on a case table: every verdict (fits, does-not-fit, partial-offload, missing, tool-absent, unpinned), the trained-ctx floor read from a GGUF header (v2/v3, array skip, truncated, non-GGUF), and bad inputs.
• Parity harness scripts/tests/ci_tools_py_parity_test.sh gains the cases; cargo-mutants on the module: 0 missed.
• The .py and its callers stay (N-1): scripts/model_ladder.sh is on a certification gate path, and scripts/check_model_ladder.sh mutates the .py in its self-test. They switch once a released aprender-ci-tools carries the port.