fix(bedrock): add live model discovery and region resolution for non-US regions

provider_model_ids("bedrock") fell through to a static _PROVIDER_MODELS
table containing only hardcoded us.* model IDs.  Users configured for
non-US AWS regions (eu-central-1, ap-northeast-1, etc.) saw wrong or no
models in /model and autocomplete.

Root causes fixed:

1. models.py: provider_model_ids() now calls discover_bedrock_models()
   keyed by the resolved region before falling back to the static table.
   A new bedrock_model_ids_or_none() helper in bedrock_adapter.py
   consolidates the discover -> extract IDs -> fallback pattern used by
   all three call sites.

2. providers.py: registers bedrock in HERMES_OVERLAYS with
   transport=bedrock_converse and auth_type=aws_sdk so
   get_provider("bedrock") and resolve_provider_full("bedrock") work.

3. model_switch.py: list_authenticated_providers() sections 2 and 3
   detect AWS credentials via has_aws_credentials() for aws_sdk
   overlays and use live discovery for the model list.

4. bedrock_adapter.py: resolve_bedrock_region() reads the configured
   region from botocore.session before falling back to us-east-1,
   covering users who set their region in ~/.aws/config via a named
   profile rather than env vars.

5. tui_gateway/server.py: passes provider= to get_model_context_length()
   so context window lookups work correctly for the Bedrock provider.

hermes_cli/models.py

@@ -1988,6 +1988,18 @@ def provider_model_ids(provider: Optional[str], *, force_refresh: bool = False)
             live = fetch_api_models(api_key, base_url)
             if live:
                 return live
+    # Bedrock uses live discovery keyed by the resolved AWS region so that
+    # EU/AP users see eu.*/ap.* model IDs instead of the static us.* list.
+    # Note: early return intentionally skips _MODELS_DEV_PREFERRED merge
+    # below — bedrock is not expected to appear in that table.
+    if normalized == "bedrock":
+        try:
+            from agent.bedrock_adapter import bedrock_model_ids_or_none
+            ids = bedrock_model_ids_or_none()
+            if ids is not None:
+                return ids
+        except Exception:
+            pass
     curated_static = list(_PROVIDER_MODELS.get(normalized, []))
     if normalized in _MODELS_DEV_PREFERRED:
         return _merge_with_models_dev(normalized, curated_static)