fix(migrate): analyze current cron job format

[RerankerGuo]

Summary

• read current OpenClaw cron files from their jobs array
• retain support for legacy top-level job arrays
• emit genuinely empty dependency categories as [], not [""]
• add end-to-end analysis regressions for both cron formats and an empty environment

Problem

generate-zip.sh already documents the current cron schema as {"version":1,"jobs":[...]}, but analyze.sh still evaluates .[].payload... as if the root were a job array. jq errors are intentionally suppressed by the heuristic scanner, so current-format cron commands silently disappear from tool-analysis.json and their required binaries are omitted from migration planning.

The JSON serialization also pipes empty Bash arrays through printf, which emits one blank line and turns every empty dependency category into [""]. That pollutes the analysis report and downstream migration manifest with a fake package/binary entry.

Testing

• the regression reports cron_payload_commands: 0 and misses the cron-only binary on current main
• an empty baseline analysis produces [""] for apt, pip, npm, and unknown binaries; the fixed output uses []
• bash migrate/skill/tests/test-analyze-cron.sh
• shellcheck -S warning migrate/skill/tests/test-analyze-cron.sh
• bash -n migrate/skill/scripts/analyze.sh migrate/skill/tests/test-analyze-cron.sh
• git diff --check

The test verifies current object-wrapped jobs, legacy top-level arrays, and an environment with no detected dependencies. This is separate from #1048, which only corrects the final generated import command.

[shiyiyue1102]

LGTM. The analyzer now supports both the current object-wrapped cron format and the legacy top-level array, and empty dependency categories serialize as real empty arrays. The change is scoped, includes focused regression coverage, and the required check is green.