feat: add ATIF trajectory export

[minixalpha]

Summary

• add an opt-in --trajectory PATH interface for headless runs that exports one complete ATIF-v1.7 JSON document without changing text stdout
• project user and model steps, tool calls and observations, token/cache metrics, timestamps, durations, model metadata, and terminal outcomes from the internal Event Journal
• write trajectory files atomically with owner-only permissions, reject existing paths and stdout targets, and preserve partial failed runs
• expose Event Journal truncation metadata on affected ATIF steps, tool calls, observations, and terminal data so shortened fields are never presented as complete
• add Harbor 0.21.0 validator coverage and document the interface in both READMEs, the changelog, and synchronized Chinese/English development notes

Validation

• uv run pytest — 174 passed
• uv run --project benchmarks/harbor pytest benchmarks/harbor/tests/test_atif_compatibility.py — 1 passed
• Harbor trajectory validator accepted a generated ATIF-v1.7 fixture trajectory
• git diff --check