fix(sources): ladder STRESS_SCORE so the source collapse stays deterministic

STRESS_SCORE has no source-priority ladder, so metricKeyForType returns null
and the SQL source collapse falls to an alphabetical rank-90 tiebreak. It is
safe today because the only producer is the COMPUTED HRV-derived proxy, but
the instant a device-native producer (Oura daily_stress) is enabled both rows
survive and blend nondeterministically.

Add a stress metric key with an OURA-above-COMPUTED default ladder, wire it
through metricKeyForType and RANKED_TYPES, and surface it in the Sources
settings (all six locales). A guard test asserts every RANKED_TYPES member
resolves to a non-null metric key so a future ranked type can't ship unladdered.
Regenerate the OpenAPI for the additive source-priority key.

docs/api/openapi.yaml

@@ -3606,6 +3606,22 @@ paths:
                       - NIGHTSCOUT
                       - POLAR
                       - OURA
+                stress:
+                  maxItems: 8
+                  type: array
+                  items:
+                    type: string
+                    enum:
+                      - MANUAL
+                      - WITHINGS
+                      - IMPORT
+                      - APPLE_HEALTH
+                      - COMPUTED
+                      - WHOOP
+                      - FITBIT
+                      - NIGHTSCOUT
+                      - POLAR
+                      - OURA
                 metricPriority:
                   type: object
                   properties:
@@ -3881,6 +3897,22 @@ paths:
                           - NIGHTSCOUT
                           - POLAR
                           - OURA
+                    stress:
+                      maxItems: 8
+                      type: array
+                      items:
+                        type: string
+                        enum:
+                          - MANUAL
+                          - WITHINGS
+                          - IMPORT
+                          - APPLE_HEALTH
+                          - COMPUTED
+                          - WHOOP
+                          - FITBIT
+                          - NIGHTSCOUT
+                          - POLAR
+                          - OURA
                 deviceTypePriority:
                   type: object
                   properties:
@@ -14406,6 +14438,22 @@ components:
                   - NIGHTSCOUT
                   - POLAR
                   - OURA
+            stress:
+              maxItems: 8
+              type: array
+              items:
+                type: string
+                enum:
+                  - MANUAL
+                  - WITHINGS
+                  - IMPORT
+                  - APPLE_HEALTH
+                  - COMPUTED
+                  - WHOOP
+                  - FITBIT
+                  - NIGHTSCOUT
+                  - POLAR
+                  - OURA
             metricPriority:
               type: object
               properties:
@@ -14681,6 +14729,22 @@ components:
                       - NIGHTSCOUT
                       - POLAR
                       - OURA
+                stress:
+                  maxItems: 8
+                  type: array
+                  items:
+                    type: string
+                    enum:
+                      - MANUAL
+                      - WITHINGS
+                      - IMPORT
+                      - APPLE_HEALTH
+                      - COMPUTED
+                      - WHOOP
+                      - FITBIT
+                      - NIGHTSCOUT
+                      - POLAR
+                      - OURA
               additionalProperties: false
             deviceTypePriority:
               type: object
@@ -15002,6 +15066,22 @@ components:
                   - NIGHTSCOUT
                   - POLAR
                   - OURA
+            stress:
+              maxItems: 8
+              type: array
+              items:
+                type: string
+                enum:
+                  - MANUAL
+                  - WITHINGS
+                  - IMPORT
+                  - APPLE_HEALTH
+                  - COMPUTED
+                  - WHOOP
+                  - FITBIT
+                  - NIGHTSCOUT
+                  - POLAR
+                  - OURA
             metricPriority:
               type: object
               properties:
@@ -15277,6 +15357,22 @@ components:
                       - NIGHTSCOUT
                       - POLAR
                       - OURA
+                stress:
+                  maxItems: 8
+                  type: array
+                  items:
+                    type: string
+                    enum:
+                      - MANUAL
+                      - WITHINGS
+                      - IMPORT
+                      - APPLE_HEALTH
+                      - COMPUTED
+                      - WHOOP
+                      - FITBIT
+                      - NIGHTSCOUT
+                      - POLAR
+                      - OURA
               additionalProperties: false
             deviceTypePriority:
               type: object