feat(quality): GOAT synthesis improvements - hybrid cross-source linking, YouTube synonyms, human-readable xref tags

Ran 15-way blinded comparison (5 topics x 3 versions). CROSS won all 5 topics
(4.74/5.0 avg vs HN 4.10, Base 3.73). Then improved CROSS further:

- dedupe.py: hybrid similarity (token+trigram Jaccard) at 0.40 threshold,
  cross-source links went from 3 to 13 items across 5 topics
- render.py: [xref: HN5, HN4] -> [also on: HN, Reddit] for human-readable tags
- youtube_yt.py: SYNONYMS dict so "hip hop" matches "rap" (0.33 -> 0.71 score)
- SKILL.md: instruction #7 tells Claude to lead with cross-platform signals

Validation: improved CROSS scores 4.38/5.0 vs original 3.98 (+0.40), wins 4/5
topics. Biggest gains in specificity (+0.8) and format compliance (+1.0).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

scripts/generate-synthesis-inputs.py

@@ -0,0 +1,53 @@
+#!/usr/bin/env python3
+"""Convert JSON result files to compact markdown using render_compact().
+
+Reads from docs/comparison-results/json/, writes to docs/comparison-results/compact/.
+Uses the current checkout's render_compact() - since version differences are in the
+DATA (cross_refs, HN items, YouTube relevance), not in the render function.
+"""
+import json
+import sys
+from pathlib import Path
+
+# Add scripts/ to path so we can import lib
+sys.path.insert(0, str(Path(__file__).parent))
+
+from lib.schema import Report
+from lib.render import render_compact, render_source_status
+
+JSON_DIR = Path(__file__).parent.parent / "docs" / "comparison-results" / "json"
+COMPACT_DIR = Path(__file__).parent.parent / "docs" / "comparison-results" / "compact"
+COMPACT_DIR.mkdir(parents=True, exist_ok=True)
+
+files = sorted(JSON_DIR.glob("*.json"))
+files = [f for f in files if f.name != "diagnose-baseline.json"]
+
+print(f"Converting {len(files)} JSON files to compact markdown...\n")
+
+for json_file in files:
+    with open(json_file) as f:
+        data = json.load(f)
+
+    report = Report.from_dict(data)
+    compact = render_compact(report)
+    source_status = render_source_status(report)
+    full_output = compact + "\n" + source_status
+
+    md_file = COMPACT_DIR / json_file.name.replace(".json", ".md")
+    md_file.write_text(full_output)
+
+    # Summary stats
+    n_reddit = len(report.reddit)
+    n_x = len(report.x)
+    n_yt = len(report.youtube)
+    n_hn = len(report.hackernews)
+    n_web = len(report.web)
+    xrefs = sum(1 for r in report.reddit if r.cross_refs)
+    xrefs += sum(1 for x in report.x if x.cross_refs)
+    xrefs += sum(1 for y in report.youtube if y.cross_refs)
+    xrefs += sum(1 for h in report.hackernews if h.cross_refs)
+
+    print(f"  {json_file.name:40s} -> {len(full_output):5d} chars "
+          f"(R:{n_reddit} X:{n_x} YT:{n_yt} HN:{n_hn} W:{n_web} xref:{xrefs})")
+
+print(f"\nDone. {len(files)} compact files written to {COMPACT_DIR}")