feat: add native Anthropic API provider support

- Implement new anthropicClient with full Client interface
- Add Streamer interface for token-by-token streaming via SSE
- Add Anthropic Messages API v1 integration with proper headers
- Support claude-3-5-sonnet-20241022 as default model
- Add configuration via [anthropic] TOML section
- Add environment variable overrides (HEXAI_ANTHROPIC_*)
- Support both HEXAI_ANTHROPIC_API_KEY and ANTHROPIC_API_KEY fallback
- Integrate Anthropic key handling in LSP, CLI, and llmutils
- Update provider factory to support 'anthropic' provider name
- Add 11 comprehensive unit tests for Anthropic client
- Update config.toml.example with [anthropic] section
- Update NewFromConfig() signature to accept anthropicAPIKey parameter
- All 51 internal LLM tests pass (11 new Anthropic tests + 40 existing)

Anthropic models can be accessed via:
  [anthropic]
  model = "claude-3-5-sonnet-20241022"
  base_url = "https://api.anthropic.com/v1"
  temperature = 0.2

  or environment:
  export HEXAI_PROVIDER="anthropic"
  export HEXAI_ANTHROPIC_API_KEY="your-key"

Amp-Thread-ID: https://ampcode.com/threads/T-019c0af1-f215-72cf-9940-b014b1a9576b
Co-authored-by: Amp <amp@ampcode.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/internal/llm/provider_more_test.go b/internal/llm/provider_more_test.go
index eff99e6..caad912 100644
--- a/internal/llm/provider_more_test.go
+++ b/internal/llm/provider_more_test.go
@@ -16,13 +16,13 @@ func TestWithOptions_Apply(t *testing.T) {
 func TestNewFromConfig_Success_OpenAI_And_Copilot(t *testing.T) {
 	// OpenAI success
 	oc := Config{Provider: "openai", OpenAIBaseURL: "http://x", OpenAIModel: "gpt"}
-	c, err := NewFromConfig(oc, "KEY", "", "")
+	c, err := NewFromConfig(oc, "KEY", "", "", "")
 	if err != nil || c == nil || c.Name() != "openai" || c.DefaultModel() == "" {
 		t.Fatalf("openai new: %v %v", c, err)
 	}
 	// Copilot success
 	cc := Config{Provider: "copilot", CopilotBaseURL: "http://x", CopilotModel: "gpt-4o-mini"}
-	c2, err := NewFromConfig(cc, "", "", "KEY")
+	c2, err := NewFromConfig(cc, "", "", "KEY", "")
 	if err != nil || c2 == nil || c2.Name() != "copilot" || c2.DefaultModel() == "" {
 		t.Fatalf("copilot new: %v %v", c2, err)
 	}