Remove picture id from reference nodes

REFERENCE_SYSTEM_SPEC.md

@@ -119,8 +119,10 @@ For locations:
   - Optional list of alternate match names.
 
 - `picture_id`
-  - Optional integer representing the intended `<Picture N>` identity.
-  - This is authoring metadata, not the final socket position.
+  - Optional integer representing the effective `<Picture N>` identity.
+  - It is inferred by consumer nodes such as `Dumas H3 Long Videos` from the
+    connected socket position when that position is known.
+  - Producer nodes do not need a manual `picture_id` input.
 
 - `picture_label`
   - Derived convenience text like `<Picture 1>`.
@@ -167,7 +169,6 @@ Recommended name:
 Inputs:
 
 - `image`
-- `picture_id`
 - `character_id`
 - `name`
 - `alias`
@@ -202,7 +203,6 @@ Recommended name:
 Inputs:
 
 - `image`
-- `picture_id`
 - `location_id`
 - `name`
 - `alias`
@@ -383,4 +383,3 @@ That is the change that removes the current ambiguity between:
 - character identity
 - wardrobe data
 - location / environment description
-