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/ui/acp/src/index.ts

@@ -115,8 +115,6 @@ function sameWorkspaceCwd(left: string, right: string): boolean {
 export interface AcpConfig {
   /** Model name for created agents (must have a registered adapter). */
   model?: string
-  /** Per-agent system prompt. */
-  systemPrompt?: string
   /**
    * Transport stream override. Production omits this (the plugin wires
    * `process.stdin`/`process.stdout` via `ndJsonStream`). Tests inject an
@@ -129,7 +127,6 @@ export interface AcpConfig {
 
 export const Config: Schema<AcpConfig> = Schema.object({
   model: Schema.string(),
-  systemPrompt: Schema.string(),
 })
 
 /**
@@ -705,10 +702,9 @@ export function apply(ctx: Context, config: AcpConfig): void {
  * (exactOptionalPropertyTypes: never assign `undefined` to an optional key).
  * Exported for unit coverage of both the present and absent branches.
  */
-export function agentOptions(config: AcpConfig): { model?: string; systemPrompt?: string } {
+export function agentOptions(config: AcpConfig): { model?: string } {
   return {
     ...config.model !== undefined ? { model: config.model } : {},
-    ...config.systemPrompt !== undefined ? { systemPrompt: config.systemPrompt } : {},
   }
 }