Adds a new 'Auxiliary Capacity-Error Fallback' section to
website/docs/user-guide/features/fallback-providers.md covering:
- The 4-step ladder (primary → fallback_chain → main agent → warn)
- Which errors trigger fallback (402, 429 quota, connection) vs
which respect explicit provider choice (transient 429 rate limits)
- Optional fallback_chain config schema with vision + compression examples
- Recognized quota-error phrases (Bedrock, Vertex AI, generic)
Updates the bottom summary table — every auxiliary task now shows
'Layered (see above)' instead of 'Auto-detection chain' since
explicit-provider users also get the main-agent safety net.
43e566f77e