Introduces anyllm_providers crate as metadata-only catalog (ProviderDef,
ModelDef, registry). Wires any provider-id as BACKEND via OpenAIClient.
Adds bedrock_native.rs (Converse/InvokeModel with SigV4) and
generic_passthrough.rs catch-all for Translate mode. Updates config,
backend clients, streaming, token counting, and compatibility tests
to support the expanded provider surface. Updates model pricing and docs.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>