review: the persona becomes the system-prompt plugin's deployment config

Review round 2 (tianyicui inline comments):

- dsh-system-prompt itself registers the harness:identity (-100) and
  deployment:persona (0) sections — they must survive a swapped loop
  plugin, so they leave dsh-agent-loop; the persona text is the plugin's
  own validated 'persona' config. The model/cwd variables STAY on the
  loop: runtime facts of the agents it drives.
- AgentOptions.systemPrompt is deleted with all its forwarding plumbing:
  the app configs' systemPrompt keys become 'persona' routed through
  dsh-agent-core (schema = z.intersect of the owners'), the ACP bridge
  and tool-subagent stop carrying persona configuration, and subagent
  children now render the deployment persona like every other agent.
- Example personas drop transport/interface trivia (ACP, CLI) — facts
  irrelevant to the model.
- Root CONTEXT.md removed (not idiomatic); its persona definition was
  wrong under the new ownership anyway.
- Docs, READMEs, the prompt-variables RFC, and generated catalogs
  updated; new loop test pins the assemble-waterfall escape valve
  (an emptied assembly sends NO system field).

packages/core/agent/src/index.ts

@@ -49,7 +49,7 @@ export interface CreateAgentOptions {
    * for a fresh (spawn) child.
    */
   seed?: SessionEvent[]
-  /** Per-agent options (model, system prompt). */
+  /** Per-agent options (model, …). */
   agentOptions?: AgentOptions
 }
 
@@ -62,7 +62,7 @@ export interface ResumeAgentOptions {
   agentId: AgentId
   /** The persisted session id to load and resume on. */
   resumeSessionId: SessionId
-  /** Per-agent options (model, system prompt). */
+  /** Per-agent options (model, …). */
   agentOptions?: AgentOptions
 }