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).

docs/cordis-catalog/services.md

@@ -180,7 +180,7 @@ Source: [`packages/subagent/subagent/src/index.ts:142`](../../packages/subagent/
 
 ## `ctx.systemPrompt` — `SystemPrompt`
 
-Registry service (`ctx.systemPrompt`): plugins contribute ordered text sections, tool-schema providers, and named prompt variables; the agent loop calls `assemble(context)` once per step.
+Registry service (`ctx.systemPrompt`): plugins contribute ordered text sections, tool-schema providers, and named prompt variables; the agent loop calls `assemble(context)` once per step. Registers the harness-owned `harness:identity` and `deployment:persona` sections itself (see Config.persona).
 
 ```ts cordis-catalog
 section(section: PromptSection): () => void
@@ -189,7 +189,7 @@ variable(name: string, provider: (context: AssembleContext) => string | undefine
 assemble(context: AssembleContext = {}): Promise<PromptAssembly>
 ```
 
-Source: [`packages/core/system-prompt/src/index.ts:174`](../../packages/core/system-prompt/src/index.ts)
+Source: [`packages/core/system-prompt/src/index.ts:198`](../../packages/core/system-prompt/src/index.ts)
 
 ## `ctx.tools` — `ToolRegistry`