fix: resolve remaining shell syntax in run() calls (closes #110)

[TerminalGravity]

Problem

After the execFileSync migration, 8 tool files still passed shell syntax (pipes, redirects, non-git binaries like wc, find, cat, head, tail, command -v, gh) to run(), which wraps execFileSync('git', args). These commands silently fail because shell operators become literal git arguments.

Solution

Option 3 from #110: both approaches.

1. Added shell() helper in git.ts — uses execSync for commands that genuinely need shell features (pipes, redirects, non-git binaries)
2. Converted simple git commands to proper array args where no shell features are needed

Files fixed (all 8 from the issue)

• verify-completion.ts — cat, tsc | tail, build | tail
• token-audit.ts — wc -l, wc -c, tail -c, git diff → array args
• clarify-intent.ts — tsc | grep, find | head
• session-handoff.ts — command -v, gh pr list || echo
• audit-workspace.ts — git diff → array args, find | wc -l
• enrich-agent-task.ts — git ls-files | grep, head -30
• scope-work.ts — git ls-files | head | grep
• sequence-tasks.ts — git ls-files | head

Build clean, all 43 tests pass.

Closes #110

[TerminalGravity]

CI is green on this one ✅. However, looking at #120, it covers 4 additional files that this PR misses (checkpoint.ts, session-health.ts, sharpen-followup.ts, what-changed.ts). If we go with #119 we'd still have shell syntax lurking in those files.

Recommendation: either expand this PR to cover those 4 files too, or let #120 be the canonical fix once its CI passes. As-is, #120 is the more complete solution.