feat(mcpd+deploy): serve web UI at /ui + smoke tests + docs (Stage 6)

The closing stage. mcpd now hosts the Stage 5 SPA, the Docker image
bundles the build artifact, a smoke test exercises the personality
HTTP surface end-to-end, and the user-facing docs spell out the
mental model.

mcpd:
- Add @fastify/static dep.
- New routes/web-ui.ts: registers /ui/* against a static bundle. Looks
  for the bundle at $MCPD_WEB_ROOT, then /usr/share/mcpd/web (the
  Docker image path), then a dev-tree fallback. Logs and skips
  cleanly if missing — API-only deploys keep working.
- SPA fallback: any /ui/<path> that doesn't match a file falls through
  to index.html so direct hits to react-router URLs work.
- /ui/* falls through to `kind: skip` in mapUrlToPermission, so the
  static assets are served unauthenticated. Each API call from the
  SPA still carries the bearer token.

Deploy:
- Dockerfile.mcpd builds the @mcpctl/web bundle in the same builder
  stage and copies dist/ to /usr/share/mcpd/web in the runtime image.

Smoke (personality.smoke.test.ts):
- Live mcpd flow: create secret/llm/agent/personality, attach an
  agent-direct prompt, verify the binding listing, reject double-
  attach (409) + foreign-agent prompt (400), set defaultPersonality
  by name, detach + delete cleanup.

Docs:
- New docs/personalities.md: VLAN-on-ethernet model, system-block
  ordering table, three prompt scopes, CLI walkthrough, web UI
  walkthrough, full API surface, RBAC notes.
- agents.md and chat.md cross-link.
- README's Agents section gains a Personalities subsection.

Test count after Stage 6:
  mcpd:   801/801      cli:  430/430
  web:    7/7          db:   58/62 (4 pre-existing)

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

docs/chat.md

@@ -27,6 +27,8 @@ back to the agent.
 --system <text>              # replace agent.systemPrompt for this session
 --system-file <path>         # read --system text from a file
 --system-append <text>       # append to the agent system block (after project Prompts)
+--personality <name>         # apply a personality overlay for this turn
+                             # (additive — see docs/personalities.md)
 --temperature <n>            # 0..2
 --top-p <n>                  # 0..1
 --top-k <n>                  # integer; Anthropic-only, OpenAI ignores