Document v3.1.2 conventions: dedup scoping and sentinel values

Two micro-risk mitigations documented:

1. dedup_group_id: Format "{business_id}:{hash}" to prevent
   cross-tenant collision on similar reviews.

2. Sentinel conventions: 'ALL' (spatial) vs 'all' (semantic).
   Case matters — do not normalize.

Spec frozen as v3.1.2.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.artifacts/ReviewIQ-Architecture-v3.1.md

@@ -233,7 +233,7 @@ CREATE TABLE reviews_enriched (
 
     -- Quality control
     trust_score         FLOAT DEFAULT 1.0,      -- 0.0 to 1.0
-    dedup_group_id      TEXT,                   -- Groups duplicate/near-duplicate reviews
+    dedup_group_id      TEXT,                   -- Tenant-scoped: format "{business_id}:{hash}"
     is_suspicious       BOOLEAN DEFAULT FALSE,
 
     -- Processing metadata
@@ -405,7 +405,11 @@ CREATE INDEX idx_events_review ON issue_events(source, review_id, review_version
 
 ### 2.4 Unified Analytics Spine
 
-**Design Decision**: `place_id = 'ALL'` is the sentinel for "all locations" rollups. This avoids NULL handling complexity while keeping the schema simple.
+**Design Decision**: Sentinel value conventions (do not normalize):
+- `place_id = 'ALL'` — spatial rollup (all locations)
+- `subject_id = 'all'` — semantic rollup (all subjects within type)
+
+Case matters: `'ALL'` ≠ `'all'`. This avoids NULL handling while keeping the schema simple.
 
 ```sql
 -- Fact table: pre-aggregated time-series metrics