feat(provider): add Ollama client implementation in new providers crate

- Introduce `owlen-providers` crate with Cargo.toml and lib entry.
- Expose `OllamaClient` handling HTTP communication, health checks, model listing, and streaming generation.
- Implement request building, endpoint handling, and error mapping.
- Parse Ollama tags response and generation stream lines into core types.
- Add shared module re-exports for easy integration with the provider layer.

Cargo.toml

@@ -4,6 +4,7 @@ members = [
     "crates/owlen-core",
     "crates/owlen-tui",
     "crates/owlen-cli",
+    "crates/owlen-providers",
     "crates/owlen-mcp-server",
     "crates/owlen-mcp-llm-server",
     "crates/owlen-mcp-client",