Fix
- providers: retry only genuinely-transient Ollama transport errors
- providers: log a failed Ollama batch once, not once per retry attempt
- providers: log the batch shape on every Ollama embed failure
- providers: give Ollama the transient retry every other provider has
- providers: bound Ollama embed requests by characters, not item count
- vector: clear the dead-letter marker only after the upsert succeeds
- vector: dead-letter documents after repeated index failures