feat(import): add CodeTraceBench bulk conversion

[drewstone]

What changed

• add traces import-codetracebench for official CodeTracer-normalized trajectories
• preserve upstream step ids as step-<n> OTLP spans without importing labels
• reject annotation leakage, unsafe paths, duplicate ids, malformed rows, and mismatched step counts
• publish atomically with an adjacent ownership lock and a receipt containing input and output SHA-256 hashes
• expose the importer through the SDK and document the CLI entry point

Why

agent-eval analyst-benchmark needs one deterministic, label-free trace per public trajectory. This imports the maintained upstream normalization output instead of duplicating CodeTracer parsers.

Proof

• pnpm typecheck
• pnpm test: 394/394 tests passed across 34 files
• pnpm build
• pnpm check:package: packed CLI and 2 skills passed
• git merge-tree --write-tree origin/main HEAD
• git diff origin/main...HEAD --check
• two concurrent importers: exactly one output owner; the loser writes no output files
• 32 public compatibility cases: 32 traces, 935 action steps, 1,897 spans, zero label leaks or hash mismatches

The 32-case input is a compatibility-filtered calibration set, not a leaderboard sample.