feat: proper error handling replacing silent suppression (DOJ-2429)

[dbejarano820]

Summary

• Added log_error(), json_escape(), and check_jq() helpers
• Replaced 2>/dev/null with error capture + logging + fallback
• Error log at ~/.code-sensei/error.log, auto-capped at 1000 lines
• One-time jq-missing warning per session
• All dynamic strings in JSON output use json_escape()

Test plan

• bash -n passes on all scripts
• Scripts still exit 0 on errors
• Error log captures failures with timestamps
• No silent error suppression without fallback

Closes DOJ-2429

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[dbejarano820]

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