Adopt narrow helper exception boundaries

[vibeforge1111]

Summary

Maintainer adoption of four small Spark Compete source PRs that narrow helper exception handling without changing trust boundaries.

Source PR credit:

• Credits [spark-compete] Narrow bare except in read_json + read_toml helpers in system_map.py to their exhaustive parse + OS error classes #532: read_json / read_toml catch parse and OS errors instead of broad Exception.
• Credits [spark-compete] Narrow bare except in inspect_spawner_prd_auto_trace JSONL scanner to (json.JSONDecodeError) + (OSError) #533: Spawner PRD trace scanner catches JSON decode errors per-line and OS errors around file access.
• Credits [spark-compete] Narrow bare except in git_summary + run_git subprocess helpers in system_map.py to (subprocess.SubprocessError, OSError) #534: git helper subprocess failures catch subprocess.SubprocessError / OSError.
• Credits [spark-compete] Narrow bare except in revoke-all active-mission pause save_json wrapper to OSError #528: revoke-all active mission pause write failure catches OSError.

No participant credit should be assigned to this maintainer adoption PR itself.

Verification

• python -m pytest tests\\test_system_map.py -q -k json_toml_git_spawner_trace
• python -m pytest tests\\test_cli.py -q -k security_revoke_all_os_error
• python -m pytest tests\\test_system_map.py -q
• python -m pytest tests\\test_cli.py -q
• python -m compileall src
• git diff --check
• python -m spark_cli.cli verify --registry-pins --json

Risk

Low. This narrows catches around expected parse, IO, subprocess, and SQLite-adjacent support paths, with regression tests. It does not change installer metadata, registry pins, scoring, secrets, auth, sandbox policy, provider behavior, or network allow/deny rules.