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, 1 insertions, 1 deletions

diff --git a/internal/llm/provider_more2_test.go b/internal/llm/provider_more2_test.go
index e001e5c..86b149a 100644
--- a/internal/llm/provider_more2_test.go
+++ b/internal/llm/provider_more2_test.go
@@ -5,7 +5,7 @@ import "testing"
 func TestNewFromConfig_Copilot(t *testing.T) {
 	t.Setenv("COPILOT_API_KEY", "x")
 	cfg := Config{Provider: "copilot", CopilotModel: "small"}
-	c, err := NewFromConfig(cfg, "", "", "x")
+	c, err := NewFromConfig(cfg, "", "", "x", "")
 	if err != nil || c == nil {
 		t.Fatalf("copilot provider failed: %v %v", c, err)
 	}