feat: virtual-LLM smoke test + docs (v1 Stage 6)

Final stage of v1.

Smoke (mcplocal/tests/smoke/virtual-llm.smoke.test.ts):
- Spins an in-process LlmProvider that returns canned content.
- Runs the registrar against the live mcpd in fulldeploy.
- Asserts: row appears with kind=virtual / status=active, infer
  through /api/v1/llms/<name>/infer comes back through the SSE
  relay with the provider's content + finish_reason, and a 503
  appears immediately after registrar.stop() (publisher offline).
- Times out / cleanup paths idempotent so re-runs against the same
  cluster don't litter rows. The 90-s heartbeat-stale flip and 4-h
  GC are unit-tested — too slow for smoke.

Docs:
- New docs/virtual-llms.md: when to use this vs creating a regular
  Llm row, how to opt-in via publish: true, the lifecycle table,
  the inference-relay sequence, the v1 streaming caveat, the v2-v5
  roadmap, and the full /api/v1/llms/_provider-* surface.
- agents.md cross-links virtual-llms.md alongside personalities/chat.
- README's Agents section gains a "Virtual LLMs" subsection.

Workspace suite: 2043/2043 (smoke files run separately). v1 closes.

Stage roadmap (each its own future PR):
  v2 wake-on-demand · v3 virtual agents · v4 LB pool · v5 task queue

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.md

@@ -571,6 +571,32 @@ For binding prompts to personalities and the API surface, see
 prompt editing — paste a session token (`mcpctl auth login`) or PAT to log
 in.
 
+### Virtual LLMs
+
+A user's local LLM (`vllm-local`, Ollama, …) can publish itself into
+mcpd's `Llm` registry so anyone authorized sees it under `mcpctl get llm`
+and can chat with it via `mcpctl chat-llm <name>`. Inference is relayed
+through the publishing mcplocal's SSE control channel — mcpd never holds
+the local URL or API key.
+
+```fish
+# In ~/.mcpctl/config.json, opt the provider in with `publish: true`:
+#   { "name": "vllm-local", "type": "openai", "model": "...", "publish": true }
+systemctl --user restart mcplocal
+
+mcpctl get llm
+# NAME             KIND     STATUS    TYPE     MODEL                          TIER  ID
+# qwen3-thinking   public   active    openai   qwen3-thinking                 fast  ...
+# vllm-local       virtual  active    openai   Qwen/Qwen2.5-7B-Instruct-AWQ   fast  ...
+
+mcpctl chat-llm vllm-local
+> hello?
+```
+
+Lifecycle: 30 s heartbeats, 90 s heartbeat-stale → inactive, 4 h
+inactive → auto-deleted. A reconnecting mcplocal adopts the same row
+via a sticky `providerSessionId`. Full design: [docs/virtual-llms.md](docs/virtual-llms.md).
+
 ## Commands
 
 ```bash