docs(adr): clarify result row sidecar identity

[christso]

Summary

Reconciles the accepted result-layout ADRs with the final merged layout from PR #1558: an AgentV invocation writes under .agentv/results/<experiment>/<timestamp>/, and each target plus optional variant gets its own nested result bundle with index.jsonl, summary.json, and deterministic <row_id>/run-1, <row_id>/run-2, etc. sidecars.

This keeps experiment as the campaign namespace and the timestamp as the invocation/batch folder, while making the target/variant folders storage isolation and manual browsing aids only. Dashboard and readers discover nested index.jsonl manifests, then use manifest and row metadata for target, variant, eval path, suite, and test identity semantics.

Changes

• Updates ADR 0009 to document .agentv/results/<experiment>/<timestamp>/<target>/<variant?>/ bundles, each with its own index.jsonl and summary.json.
• Defines deterministic row_id directories inside each target/variant bundle, with repeated runs under run-1, run-2, and so on.
• States that legacy timestamp-level index.jsonl bundles remain readable.
• Clarifies that target, variant, eval_path, suite, and test_id semantics come from summary/index metadata, not folder-name parsing.
• Aligns ADR 0006 with ADR 0009 and removes the older imported-suite/direct-under-timestamp hierarchy guidance.
• Keeps the explicit non-goals: no rows/ parent folder, no new experiment artifact, and no hard-coded Next/Vercel semantics.

Testing

• git diff --check origin/main...HEAD
• bun run beads:check (passes with existing warning: .beads/config.yaml missing in this worktree)

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