fix: Ollama Cloud auth, /model switch persistence, and alias tab completion

- Add OLLAMA_API_KEY to credential resolution chain for ollama.com endpoints
- Update requested_provider/_explicit_api_key/_explicit_base_url after /model
  switch so _ensure_runtime_credentials() doesn't revert the switch
- Pass base_url/api_key from fallback config to resolve_provider_client()
- Add DirectAlias system: user-configurable model_aliases in config.yaml
  checked before catalog resolution, with reverse lookup by model ID
- Add /model tab completion showing aliases with provider metadata

Co-authored-by: LucidPaths <LucidPaths@users.noreply.github.com>

run_agent.py

@@ -4794,8 +4794,19 @@ class AIAgent:
         # access for Codex providers.
         try:
             from agent.auxiliary_client import resolve_provider_client
+            # Pass base_url and api_key from fallback config so custom
+            # endpoints (e.g. Ollama Cloud) resolve correctly instead of
+            # falling through to OpenRouter defaults.
+            fb_base_url_hint = (fb.get("base_url") or "").strip() or None
+            fb_api_key_hint = (fb.get("api_key") or "").strip() or None
+            # For Ollama Cloud endpoints, pull OLLAMA_API_KEY from env
+            # when no explicit key is in the fallback config.
+            if fb_base_url_hint and "ollama.com" in fb_base_url_hint.lower() and not fb_api_key_hint:
+                fb_api_key_hint = os.getenv("OLLAMA_API_KEY") or None
             fb_client, _ = resolve_provider_client(
-                fb_provider, model=fb_model, raw_codex=True)
+                fb_provider, model=fb_model, raw_codex=True,
+                explicit_base_url=fb_base_url_hint,
+                explicit_api_key=fb_api_key_hint)
             if fb_client is None:
                 logging.warning(
                     "Fallback to %s failed: provider not configured",