feat: Batch Dedup Runner — 85k→~18-25k Master Controls

Adds batch orchestration for deduplicating ~85k Pass 0b atomic controls
into ~18-25k unique masters with M:N parent linking.

New files:
- migrations/078_batch_dedup.sql: merged_into_uuid column, perf indexes,
  link_type CHECK extended for cross_regulation
- batch_dedup_runner.py: BatchDedupRunner with quality scoring, merge-hint
  grouping, title-identical short-circuit, parent-link transfer, and
  cross-regulation pass
- tests/test_batch_dedup_runner.py: 21 tests (all passing)

Modified:
- control_dedup.py: optional collection param on Qdrant functions
- crosswalk_routes.py: POST/GET batch-dedup endpoints

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

backend-compliance/migrations/078_batch_dedup.sql

@@ -0,0 +1,42 @@
+-- Migration 078: Batch Dedup — Schema extensions for 85k→~18-25k reduction
+-- Adds merged_into_uuid tracking, performance indexes for batch dedup,
+-- and extends link_type CHECK to include 'cross_regulation'.
+
+BEGIN;
+
+-- =============================================================================
+-- 1. merged_into_uuid: Track which master a duplicate was merged into
+-- =============================================================================
+
+ALTER TABLE canonical_controls
+    ADD COLUMN IF NOT EXISTS merged_into_uuid UUID REFERENCES canonical_controls(id);
+
+CREATE INDEX IF NOT EXISTS idx_cc_merged_into
+    ON canonical_controls(merged_into_uuid) WHERE merged_into_uuid IS NOT NULL;
+
+-- =============================================================================
+-- 2. Performance indexes for batch dedup queries
+-- =============================================================================
+
+-- Index on merge_group_hint inside generation_metadata (for sub-grouping)
+CREATE INDEX IF NOT EXISTS idx_cc_merge_group_hint
+    ON canonical_controls ((generation_metadata->>'merge_group_hint'))
+    WHERE decomposition_method = 'pass0b';
+
+-- Composite index for pattern-based dedup loading
+CREATE INDEX IF NOT EXISTS idx_cc_pattern_dedup
+    ON canonical_controls (pattern_id, release_state)
+    WHERE decomposition_method = 'pass0b';
+
+-- =============================================================================
+-- 3. Extend link_type CHECK to include 'cross_regulation'
+-- =============================================================================
+
+ALTER TABLE control_parent_links
+    DROP CONSTRAINT IF EXISTS control_parent_links_link_type_check;
+
+ALTER TABLE control_parent_links
+    ADD CONSTRAINT control_parent_links_link_type_check
+        CHECK (link_type IN ('decomposition', 'dedup_merge', 'manual', 'crosswalk', 'cross_regulation'));
+
+COMMIT;