feat: add OpenAI and Anthropic LLM providers

OpenAI provider supports any OpenAI-compatible API via configurable
base URL, with SSE streaming and Bearer auth. Anthropic provider uses
the Messages API with x-api-key auth and SSE event parsing. Both
include timeout handling and cancellation support.

Author: Sephyi

Cargo.lock

@@ -27,6 +27,7 @@ toml = "0.9"
 
 # Config & paths
 directories = "6.0"
+figment = { version = "0.10", features = ["toml", "env"] }
 
 # HTTP client
 reqwest = { version = "0.13", features = ["json", "stream"] }

Cargo.toml

@@ -96,6 +96,10 @@ pub struct Config {
     #[serde(default = "default_num_predict")]
     pub num_predict: u32,
 
+    /// Base URL for OpenAI-compatible APIs (default: https://api.openai.com/v1)
+    #[serde(default)]
+    pub openai_base_url: Option<String>,
+
     /// Commit message format options
     #[serde(default)]
     pub format: CommitFormat,
@@ -140,6 +144,7 @@ impl Default for Config {
             timeout_secs: default_timeout_secs(),
             temperature: default_temperature(),
             num_predict: default_num_predict(),
+            openai_base_url: None,
             format: CommitFormat::default(),
         }
     }