feat(harness): default harness wiring + env-snapshot reporting

[pradeepvrd]

The per-task run used to be a monolithic top-level loop in pkg/evaluator/evaluate.py (provision → execute agent → judge → teardown → write results); this decomposes it into devops_bench/harness/ — a default harness that wires deployer + agent + verification + metrics, resolves the agent's capabilities once, snapshots the run environment, and persists results through a pluggable reporter.

Behavior changes

• Agent capabilities are resolved once at harness construction and snapshotted, so a mid-batch env mutation cannot desync what the agent ran with from what the record reports.
• Each record carries capabilities_granted (use_mcp + skills) so consumers read what was actually granted instead of re-reading BENCH_USE_MCP.
• Results are written through the reporter both before and after scoring, so raw execution output is inspectable independent of scoring.
• chaos_spec / verification_spec accept native YAML (JSON-in-YAML strings still parse).
• Generated files are captured by diffing the workspace before/after the agent run into <run_dir>/generated_files/.

Bugs fixed

• The operator agent and the chaos injector resolve a shared default deployment + namespace at init, so they target the same workload when the relevant env vars are unset (previously they could diverge).