Add native Windows support (#91)

- Native Windows daemon using TCP loopback endpoints
- Direct-mode fallback for CLI/daemon compatibility
- Comment operations over RPC
- PowerShell installer script
- Go 1.24 requirement
- Cross-OS testing documented

Co-authored-by: danshapiro <danshapiro@users.noreply.github.com>
Amp-Thread-ID: https://ampcode.com/threads/T-c6230265-055f-4af1-9712-4481061886db
Co-authored-by: Amp <amp@ampcode.com>

internal/compact/haiku.go

@@ -22,6 +22,8 @@ const (
 	initialBackoff = 1 * time.Second
 )
 
+var ErrAPIKeyRequired = errors.New("API key required")
+
 // HaikuClient wraps the Anthropic API for issue summarization.
 type HaikuClient struct {
 	client         anthropic.Client
@@ -39,7 +41,7 @@ func NewHaikuClient(apiKey string) (*HaikuClient, error) {
 		apiKey = envKey
 	}
 	if apiKey == "" {
-		return nil, fmt.Errorf("API key required: set ANTHROPIC_API_KEY environment variable or provide via config")
+		return nil, fmt.Errorf("%w: set ANTHROPIC_API_KEY environment variable or provide via config", ErrAPIKeyRequired)
 	}
 
 	client := anthropic.NewClient(option.WithAPIKey(apiKey))