feat: regime system — Find Matching + By Regime view

- Pattern Lab: "Find Matching" button per pattern uses GPT-4o-mini to classify against library (merge_as_instance / counter_scenario / new_pattern); shows match badge + confidence + suggested #regime_tag; conditional action buttons (Merge / Save counter / Save new)
- save_pattern_from_run handles action='instance' (appends to historical_instances + updates stats), action='counter' (new pattern with counter_of link, tags parent regime_tag), action='new' (unchanged + regime_tag support)
- useApi.ts: extended useSaveLabPattern type + new useFindMatchingPattern mutation + MatchResult export type
- DB migrations: regime_tag + counter_of columns on custom_patterns
- PatternExplorer: new "By Regime" view groups saved patterns by regime_tag; RegimeCard shows historical instances, hit rate, counter-of link (orange); untagged group at bottom

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

backend/services/database.py

@@ -88,6 +88,9 @@ def init_db():
         "ALTER TABLE custom_patterns ADD COLUMN backtest_runs_count INTEGER DEFAULT 0",
         # Remove all built-in patterns (no proof of legitimacy)
         "DELETE FROM custom_patterns WHERE source = 'builtin'",
+        # Regime / counter-scenario architecture
+        "ALTER TABLE custom_patterns ADD COLUMN regime_tag TEXT",
+        "ALTER TABLE custom_patterns ADD COLUMN counter_of TEXT",
     ]:
         try:
             c.execute(_sql)