feat(mental-health): accept client source + externalId with durable dedup

The screener POST hardcoded source=WEB and ignored any client-supplied
externalId, so the native client could not tag provenance and an outbox
replay beyond the 24h idempotency-key window minted duplicate
administrations plus duplicate trend points.

Accept an optional closed source enum (WEB|IOS, default WEB) and an optional
bounded externalId, and persist both. Deduplicate on (userId, externalId)
when present: the route returns the existing administration on replay, and a
partial unique index over (user_id, external_id) WHERE external_id IS NOT
NULL (migration 0221) backstops a concurrent insert race (P2002 resolved to
the winner). The derived *_SCORE measurement keeps its stable per-assessment
externalId, so dedup at the assessment level prevents duplicate trend points.
Item answers stay encrypted and out of AI/MCP/export. Regenerate OpenAPI.

docs/api/openapi.yaml

@@ -8137,6 +8137,16 @@ paths:
                 locale:
                   type: string
                   maxLength: 16
+                source:
+                  default: WEB
+                  type: string
+                  enum:
+                    - WEB
+                    - IOS
+                externalId:
+                  type: string
+                  minLength: 1
+                  maxLength: 120
               required:
                 - instrument
                 - items