feat: add bd setup gemini for Gemini CLI integration (#845)

Add support for Gemini CLI hook-based integration, similar to Claude Code:
- bd setup gemini: Install SessionStart/PreCompress hooks
- bd setup gemini --check: Verify installation
- bd setup gemini --remove: Remove hooks
- bd setup gemini --project: Project-only installation
- bd setup gemini --stealth: Use bd prime --stealth

Also adds Gemini CLI integration check to bd doctor.

Gemini CLI's hook system is nearly identical to Claude Code's,
making this a clean, low-maintenance addition.

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

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

cmd/bd/doctor/gemini.go

@@ -0,0 +1,90 @@
+package doctor
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+)
+
+// CheckGemini returns Gemini CLI integration verification as a DoctorCheck
+func CheckGemini() DoctorCheck {
+	hasHooks := hasGeminiHooks()
+
+	if hasHooks {
+		return DoctorCheck{
+			Name:    "Gemini CLI Integration",
+			Status:  StatusOK,
+			Message: "Hooks installed",
+			Detail:  "SessionStart and PreCompress hooks enabled",
+		}
+	}
+
+	return DoctorCheck{
+		Name:    "Gemini CLI Integration",
+		Status:  StatusOK, // Not a warning - Gemini is optional
+		Message: "Not configured",
+		Detail:  "Run 'bd setup gemini' to enable Gemini CLI integration",
+	}
+}
+
+// hasGeminiHooks checks if Gemini CLI hooks are installed
+func hasGeminiHooks() bool {
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return false
+	}
+
+	globalSettings := filepath.Join(home, ".gemini", "settings.json")
+	projectSettings := ".gemini/settings.json"
+
+	return hasGeminiBeadsHooks(globalSettings) || hasGeminiBeadsHooks(projectSettings)
+}
+
+// hasGeminiBeadsHooks checks if a settings file has bd prime hooks for Gemini CLI
+func hasGeminiBeadsHooks(settingsPath string) bool {
+	data, err := os.ReadFile(settingsPath) // #nosec G304 -- settingsPath is constructed from known safe locations
+	if err != nil {
+		return false
+	}
+
+	var settings map[string]interface{}
+	if err := json.Unmarshal(data, &settings); err != nil {
+		return false
+	}
+
+	hooks, ok := settings["hooks"].(map[string]interface{})
+	if !ok {
+		return false
+	}
+
+	// Check SessionStart and PreCompress for "bd prime"
+	for _, event := range []string{"SessionStart", "PreCompress"} {
+		eventHooks, ok := hooks[event].([]interface{})
+		if !ok {
+			continue
+		}
+
+		for _, hook := range eventHooks {
+			hookMap, ok := hook.(map[string]interface{})
+			if !ok {
+				continue
+			}
+			commands, ok := hookMap["hooks"].([]interface{})
+			if !ok {
+				continue
+			}
+			for _, cmd := range commands {
+				cmdMap, ok := cmd.(map[string]interface{})
+				if !ok {
+					continue
+				}
+				cmdStr := cmdMap["command"]
+				if cmdStr == "bd prime" || cmdStr == "bd prime --stealth" {
+					return true
+				}
+			}
+		}
+	}
+
+	return false
+}