Closes #33

What

Adds a unified embedding.NewProvider factory that supports OpenAI, Ollama, and Cohere via a single ProviderConfig. Providers self-register via init() so callers only need a blank import. Custom providers can be registered at startup via RegisterFactory.

Changes

pkg/embedding/registry.go (new)

• ProviderConfig: Type, APIKey, Model, BaseURL, CacheSize
• NewProvider(cfg): resolves provider from registry, wraps in CachedProvider when CacheSize >= 0
• RegisterFactory(type, fn): registers a custom provider factory
• SupportedProviders(): returns ["openai", "ollama", "cohere"]

pkg/embedding/ollama/ (new)

• Client: calls /api/embeddings on a local Ollama server
• EmbedBatch is sequential (Ollama has no batch API)
• Default model: nomic-embed-text; default URL: http://localhost:11434
• register.go: self-registers into the factory via init()

pkg/embedding/cohere/ (new)

• Client: calls Cohere /v1/embed with input_type support
• EmbedBatch sends all texts in a single API call
• Default model: embed-english-v3.0 (1024 dims)
• Returns ErrRateLimited / ErrInvalidAPIKey on 429/401
• register.go: self-registers into the factory via init()

pkg/embedding/openai/register.go (new)

• Self-registers the existing OpenAI client into the factory

pkg/embedding/registry_test.go (new) — 5 tests: custom provider, unknown type, empty type, Ollama resolution, cache wrapping

Usage

import (
    "github.com/Siddhant-K-code/distill/pkg/embedding"
    _ "github.com/Siddhant-K-code/distill/pkg/embedding/ollama"
)

p, err := embedding.NewProvider(embedding.ProviderConfig{
    Type:  embedding.ProviderOllama,
    Model: "nomic-embed-text",
})

Compatibility

Existing cmd/ code uses openai.NewClient directly and is unaffected. The registry is additive — nothing breaks if a provider package is not imported.