docs: add REFERENCE docs, M4 workspace, Caddyfile

release/migrate_add_stranger_id.sql

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+-- Migration: Add stranger_id column for unmatched face traces
+-- Unmatched traces get stranger_id = trace_id (per-file sequential integer)
+-- Unique constraint: (file_uuid, stranger_id) WHERE stranger_id IS NOT NULL
+-- Date: 2026-05-16
+-- Usage: psql -U accusys -d momentry -f migrate_add_stranger_id.sql
+
+ALTER TABLE face_detections ADD COLUMN IF NOT EXISTS stranger_id INTEGER;
+CREATE UNIQUE INDEX IF NOT EXISTS idx_face_detections_stranger
+    ON face_detections (file_uuid, stranger_id) WHERE stranger_id IS NOT NULL;
+
+-- Assign stranger_id = trace_id for existing unmatched traces
+UPDATE face_detections SET stranger_id = trace_id
+WHERE trace_id IS NOT NULL AND identity_id IS NULL AND stranger_id IS NULL;