conductor(track): nagent_review_v3.1 restore v3 + create separate v3.1 report file

Per user directive 2026-06-20: do not overwrite the v3 main review.
- Restored nagent_review_v3_20260619.md to its v3-final content (803 lines, from commit b49be820)
- Created nagent_review_v3_1_report_20260620.md (NEW, 2900 lines) for the v3.1 thickened content
- Kept nagent_review_v3_1_20260620.md as the delta summary doc (66 lines)
- Updated metadata.json with v3_1_file_separation field documenting the file structure

The v3 main review is preserved in git history and is recoverable via 'git log -p'.

conductor/tracks/nagent_review_20260608/metadata.json

@@ -12,6 +12,12 @@
     "v3_existing_sections_renumbered": "v3's §12 Decisions / §13 Cross-references / §14 References moved to §15 / §16 / §17",
     "rationale": "Per user directive 2026-06-20: new observations belong immediately after the cluster sections (inform the decisions); the existing Decisions/Cross-references/References content is preserved and renumbered to §15-§17."
   },
+  "v3_1_file_separation": {
+    "v3_main_review_preserved": "nagent_review_v3_20260619.md (803 lines, original v3 content; NOT modified by v3.1)",
+    "v3_1_thickened_report": "nagent_review_v3_1_report_20260620.md (NEW; 2900 lines; v3.1 thickened content per the chunking strategy)",
+    "v3_1_delta_summary": "nagent_review_v3_1_20260620.md (66 lines; the delta summary doc; points to the thickened report)",
+    "user_directive_2026-06-20": "Do not overwrite the v3 report; create a separate v3.1 report file. The v3 main review is preserved in git history and is recoverable via 'git log -p -- conductor/tracks/nagent_review_20260608/nagent_review_v3_20260619.md'."
+  },
   "v3_1_chunking_strategy": {
     "main_review_loc_floor": 3800,
     "per_cluster_loc_target": "300-450",