Fix Ollama embedding indexing aborting with `"input length exceeds the context length"` (HTTP 500) by exposing a configurable `embeddings.ollama.num_ctx` setting. The new field appears on the embedding settings page when the Ollama provider is selected and ships with a default of 8192 tokens, which covers chunk sizes up to ~5000 characters for `nomic-embed-text`, `mxbai-embed-large`, `bge-m3`, and `qwen3-embedding`.
