Custom connections are gone: the CLI talks to the LLeMbas server it is logged in to

LLeMbas CLI 2.0 is LLeMbas-server-specific (CLI rule 2). Removed: the
anthropic, gemini, ollama and responses clients, context discovery and
llama-swap unloading (discover.ts), the Connection schema with its dialect,
auth, key_cmd, discover, unload_url and one_model_at_a_time, the model
`fallback` (it only ever moved to another server), effort_map and cache, and
the multi-connection refs. Kept: openai-chat, http, sse, think, effort,
tokens and all of src/lembas.

- connections.yaml holds the login (`type: webui`, as lembas login writes
  it). A custom entry from 1.x is read past with a warning that says how to
  log in, so an old file still starts; with several logins left, the latest
  is used and the others named.
- A model's ref is the id the server serves it under; the older forms
  (`<login>/<id>`, `<login>/<model>`) still resolve and config.yaml is
  rewritten once. Without a login there is no model, and the error (and the
  first-run screen, now the sign-in alone) says `lembas login <address>`.
- A login to another server signs this machine out of the previous one.
- The window is the server's word (no discovery); a capacity group comes
  from the server's `capacity.group` alone; embeddings use the server's
  /v1/embeddings.
- `lembas models` lists the server's models; install.sh's starter files, the
  README and the JSON schemas say the same.

Tests: every fixture is a login now (the fake server lists models, answers
other GETs with 404, and can hand one model to another script, as a server
with several backends); the dialect suites and the cross-connection tests are
gone with their code.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

schema/config.schema.json

@@ -3,11 +3,11 @@
   "type": "object",
   "properties": {
     "model": {
-      "description": "The model a session starts with: `connection/model`, a connection from connections.yaml and one of its models.",
+      "description": "The model a session starts with: one the LLeMbas server you are logged in to serves, by its id there (`deepseek/deepseek-flash`). Default: the server's default for your account.",
       "type": "string"
     },
     "small_model": {
-      "description": "`connection/model` for small jobs — session titles, commit messages. Default: the session's model. On a server that holds one model at a time (llama-swap), another model here swaps.",
+      "description": "The model for small jobs — session titles, commit messages, by its id on the server. Default: the session's model.",
       "type": "string"
     },
     "titles": {
@@ -866,7 +866,7 @@
       }
     },
     "embedding": {
-      "description": "Global config only. connection/model of an embedding model (OpenAI-shaped /embeddings, or Ollama): knowledge bases are then searched by meaning as well as by words. lembas kb reindex after changing it.",
+      "description": "Global config only. An embedding model the LLeMbas server serves, by its id there: knowledge bases are then searched by meaning as well as by words. lembas kb reindex after changing it.",
       "type": "string"
     },
     "effort": {