feat: adding agentic audience proposal

[emilhlauritsenWT]

SUPPORTING DOC: ARTF A.A. ADD_DATA_SEGMENT_WITH_EMBEDDINGS

Summary
This PR proposes a new ADD_DATA_SEGMENT_WITH_EMBEDDINGS intent so an ARTF agent can add OpenRTB data segments to a bid request — optionally carrying an Agentic Audiences embedding (segment[].ext.aa).

It does not invent a new bidstream carrier. It reuses the existing IAB OpenRTB Agentic Audiences community extension: provider Data.name, segment[].id / segment[].name, and the aa envelope (ver, vector, dimension, model, type) at BidRequest.user.data[].

This is a strictly additive schema extension:

Intent.ADD_DATA_SEGMENT_WITH_EMBEDDINGS = 9
Mutation.value.data_segments = 105 (DataSegmentsPayload)
Hosts and agents that do not use embeddings are unaffected. Experimental reserved ranges (1000–1999) are untouched.

Changes
proto/agenticrtbframework.proto — new intent, payload oneof field, and DataSegmentsPayload / EmbeddingData / EmbeddingSegment / AaEnvelope messages
docs/00-EXAMPLE.md — payload docs, intent table, mapping, and example mutation
Example

{
  "intent": "ADD_DATA_SEGMENT_WITH_EMBEDDINGS",
  "op": "OPERATION_ADD",
  "path": "/user/data",
  "data_segments": {
    "data": [
      {
        "name": "data-provider",
        "segment": [
          {
            "id": "seg-ctx-001",
            "name": "descriptive-name",
            "aa": {
              "ver": "1.0.0",
              "vector": "mpkZPq5HYb5SuJ4+PQrXPo/C9T7NzEy97FE4Pilcj74=",
              "dimension": 8,
              "model": "sbert-mini-ctx-001",
              "type": [2]
            }
          }
        ]
      }
    ]
  }
}