Merge polecat/Razor: tmux notifications and merge execution

Adds:
- gt mail send now triggers tmux notification for recipients
- Merge execution with config and retry logic

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/refinery/types.go

@@ -115,6 +115,41 @@ const (
 )
 
 
+// MergeConfig contains configuration for the merge process.
+type MergeConfig struct {
+	// RunTests controls whether tests are run after merge.
+	// Default: true
+	RunTests bool `json:"run_tests"`
+
+	// TestCommand is the command to run for testing.
+	// Default: "go test ./..."
+	TestCommand string `json:"test_command"`
+
+	// DeleteMergedBranches controls whether merged branches are deleted.
+	// Default: true
+	DeleteMergedBranches bool `json:"delete_merged_branches"`
+
+	// PushRetryCount is the number of times to retry a failed push.
+	// Default: 3
+	PushRetryCount int `json:"push_retry_count"`
+
+	// PushRetryDelayMs is the base delay between push retries in milliseconds.
+	// Each retry doubles the delay (exponential backoff).
+	// Default: 1000
+	PushRetryDelayMs int `json:"push_retry_delay_ms"`
+}
+
+// DefaultMergeConfig returns the default merge configuration.
+func DefaultMergeConfig() MergeConfig {
+	return MergeConfig{
+		RunTests:             true,
+		TestCommand:          "go test ./...",
+		DeleteMergedBranches: true,
+		PushRetryCount:       3,
+		PushRetryDelayMs:     1000,
+	}
+}
+
 // RefineryStats contains cumulative refinery statistics.
 type RefineryStats struct {
 	// TotalMerged is the total number of successful merges.