feat(manifold): add matcher versioning to separate legacy accepted matches from v3_outcome_guard metrics

Add MANIFOLD_MATCHER_VERSION="v3_outcome_guard" tag persisted to
manifold_match_audit.matcher_version so metrics can isolate current-matcher
stats from pre-versioning records, whose accepted matches the outcome
guard would now reject.

- schema: add matcher_version column + index; idempotent startup backfill
  tagging NULL rows as legacy_pre_outcome_guard (no outcome types) or
  v2_outcome_guard_no_version (has outcome type, version not persisted)
- save_manifold_audit: write matcher_version on every new record
- get_manifold_matches: split summary into current_version / all_time /
  legacy; recent_matches now carry matcher_version

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

api/main.py

@@ -211,16 +211,22 @@ async def get_attribution():
 
 @app.get("/api/metrics/manifold-matches")
 async def get_manifold_matches():
-    """Manifold match audit — summary stats and recent match attempts.
+    """Manifold match audit — version-split summary and recent match attempts.
 
-    summary:
-      total_accepted           — matches accepted (score >= 0.40, inversion unambiguous)
-      total_rejected           — matches rejected (low score or ambiguous inversion)
-      total_no_results         — no Manifold market found or API error
-      avg_match_score          — mean Jaccard score for accepted matches
-      trades_dominated_by_mfld — open trades where feat_mfld_lo is the largest signal
+    summary.current_version — stats for the active matcher (MANIFOLD_MATCHER_VERSION):
+      version          — the matcher version string
+      total_accepted   — matches accepted (score >= 0.40, inversion unambiguous)
+      total_rejected   — matches rejected (low score or ambiguous inversion)
+      total_no_results — no Manifold market found or API error
+      avg_match_score  — mean Jaccard score for accepted matches
+      used_in_trade    — accepted matches that were actually executed
+    summary.all_time — accepted/rejected/no_results across every matcher version.
+    summary.legacy.accepted_without_outcome_type — pre-outcome-guard accepted
+      records that the current matcher would reject (not counted in current_version).
+    summary.trades_dominated_by_mfld — open trades where feat_mfld_lo is the largest signal.
 
-    recent_matches: last 50 rows from manifold_match_audit, newest first.
+    recent_matches: last 50 rows from manifold_match_audit, newest first, each
+      tagged with matcher_version.
       used_in_trade=True only when status='accepted' AND a trade was actually executed.
     """
     data = await db.get_manifold_matches(limit=50)