feat(benchmarks): add source/sync fields and benchmark repo sync

[christso]

Closes #1232

Summary

• Extends BenchmarkEntry with optional source: { url, ref } and sync fields
• interpolateEnv() is applied to all benchmark entries on load (same as targets.yaml behavior)
• New benchmark-sync.ts module with three sync modes:
  • none (default) — no-op, path used as-is
  • oneshot — shallow git clone --depth 1 --filter=blob:none (idempotent if .git exists)
  • continuous — spawns a git-sync sidecar; fails fast with actionable error if git-sync is missing
• agentv studio / agentv serve calls syncBenchmarks() before starting the server
• agentv install git-sync — downloads a pinned version with SHA-256 verification into ~/.agentv/bin/
• agentv doctor — reports git-sync presence/absence with install hint

Before/after evidence

Before: No source/sync fields in benchmark entries; no sync capability; no agentv install/agentv doctor.

After:

# ~/.agentv/benchmarks.yaml
benchmarks:
  - id: eval-benchmarks
    name: Eval Benchmarks
    path: /srv/agentv/repo
    source:
      url: ${{ BENCHMARK_REPO_URL }}
      ref: ${{ BENCHMARK_REPO_REF:-main }}
    sync: ${{ AGENTV_SYNC:-none }}
    added_at: "2026-03-20T10:00:00Z"
    last_opened_at: "2026-03-30T14:00:00Z"

# CI/CD — fresh clone per run
AGENTV_SYNC=oneshot agentv eval my.eval.yaml

# Cloud server — continuous mirror
AGENTV_SYNC=continuous agentv studio

# Install git-sync for continuous mode
agentv install git-sync

# Check what's installed
agentv doctor

agentv doctor output (git-sync not installed):

agentv doctor

Local bin dir: /home/user/.agentv/bin

  ✗ git-sync  (not found)
      note:    Required for benchmark sync mode: continuous
      install: agentv install git-sync

Test plan

• Unit tests for resolveSyncMode, checkGitSyncInstalled, syncBenchmarkOneshot, syncBenchmarks
• Registry tests for source/sync round-trip through YAML
• Registry tests for interpolateEnv integration with ${{ BENCH_URL }}/${{ AGENTV_SYNC }}
• Existing benchmark entries without source or sync continue to work unchanged
• Full test suite passes (1766 core + 67 eval + 539 CLI)
• TypeScript typecheck passes
• Biome lint passes

🤖 Generated with Claude Code

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