v2.1.0-provider-picker: BooCoder systemd migration + provider picker

- BooCoder moves from Docker to host systemd service (boocoder.service)
- Agent dispatch (ACP + PTY) switches from SSH to direct spawn/exec
- SSH helpers marked @deprecated (kept for one release cycle)
- Provider registry (5 providers: boocode, opencode, goose, claude, qwen)
- Agent probe with direct which/exec + model discovery (qwen settings, static claude models)
- GET /api/providers route with installed status, models, transport fallback
- ProviderPicker frontend component in CoderPane header
- External provider messages route through tasks row instead of inference enqueue
- Smart scroll: MessageList only auto-scrolls when near bottom (150px threshold)
- DB: available_agents gets models, label, transport columns
- Bug fix: loadContext SELECT includes allowed_read_paths
- Bug fix: cap hit sentinel inserted before buildMessagesPayload
- docker-compose.yml: boocoder service commented out, BOOCODER_URL env var added
- CLAUDE.md: updated docs for systemd, provider registry, JSONB gotcha, loadContext

apps/coder/.env.host

@@ -0,0 +1,14 @@
+NODE_ENV=production
+PORT=9502
+HOST=100.114.205.53
+DATABASE_URL=postgres://boocode:devpass@127.0.0.1:5500/boochat
+LLAMA_SWAP_URL=http://100.101.41.16:8401
+PROJECT_ROOT_WHITELIST=/opt
+BOOTSTRAP_ROOT=/opt/projects
+DEFAULT_MODEL=qwen3.6-35b-a3b-mxfp4
+LOG_LEVEL=info
+SEARXNG_URL=http://100.114.205.53:8888
+GITEA_BASE_URL=https://git.indifferentketchup.com
+GITEA_USER=indifferentketchup
+GITEA_SSH_HOST=100.114.205.53:2222
+MCP_CONFIG_PATH=/data/mcp.json