feat(grok): Grok-native interactive runtime (opencode serve) — container side

Builds the Grok analogue of the Claude intake/secretary live-session runtime,
satisfying the same IntakeSession seam so the existing IntakeDriver loop,
message source, relay, and StreamChunk panel contract are reused unchanged:

- OpencodeServeSession: a held-open `opencode serve` session (context persists
  across turns) where each human turn is one synchronous POST /session/:id/
  message; normalize_opencode_message maps the reply parts to text/thinking/
  tool_use/draft/turn_end chunks (draft via a propose_draft tool part or the
  fenced roboco-draft fallback). Doc-verified against opencode's server API.
- grok_intake_main / grok_secretary_main: container entrypoints mirroring the
  Claude mains but yielding an OpencodeServeSession; they render opencode.json
  (xAI provider + MCP + system prompt) first, then run the receiver + driver.
- roboco-agent-grok-prompter / -secretary images (FROM roboco-agent-grok) +
  their builder services in all three compose files.

UNVERIFIED-LIVE: the opencode serve flow + exact Part schema + draft path need
a live run against grok-build-0.1 (the part mapping is defensive). The
orchestrator wiring that routes a GROK intake/secretary route to these images
is the next step (a design decision is open — see the handoff notes).

docker-compose.yaml

@@ -242,6 +242,28 @@ services:
     depends_on:
       - agent-base-image
 
+  # Interactive Grok roles (intake/secretary) — opencode-serve sessions; built
+  # FROM roboco-agent-grok, so they depend on the Grok runtime image.
+  agent-grok-prompter-image:
+    build:
+      context: .
+      dockerfile: docker/agent-grok-prompter.Dockerfile
+    image: roboco-agent-grok-prompter
+    entrypoint: ["/bin/sh", "-c", 'echo "Agent Grok Prompter image built"']
+    restart: "no"
+    depends_on:
+      - agent-grok-image
+
+  agent-grok-secretary-image:
+    build:
+      context: .
+      dockerfile: docker/agent-grok-secretary.Dockerfile
+    image: roboco-agent-grok-secretary
+    entrypoint: ["/bin/sh", "-c", 'echo "Agent Grok Secretary image built"']
+    restart: "no"
+    depends_on:
+      - agent-grok-image
+
   # ==========================================================================
   # Orchestrator - API Server + Agent Spawner
   # ==========================================================================