Add BD_AGENT_MODE for ultra-compact output

Adds agent-optimized output mode for `bd list` triggered by:
- BD_AGENT_MODE=1 environment variable (explicit)
- CLAUDE_CODE environment variable (auto-detect)

Agent mode provides:
- Ultra-compact format: just "ID: Title" per line
- Lower default limit (20 vs 50) for context efficiency
- No colors, no emojis, no pager
- Defaults to open/in_progress only (existing behavior)

(bd-x2ht)

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

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

internal/ui/styles.go

@@ -4,6 +4,7 @@ package ui
 
 import (
 	"fmt"
+	"os"
 	"strings"
 
 	"github.com/charmbracelet/lipgloss"
@@ -17,6 +18,23 @@ func init() {
 	}
 }
 
+// IsAgentMode returns true if the CLI is running in agent-optimized mode.
+// This is triggered by:
+//   - BD_AGENT_MODE=1 environment variable (explicit)
+//   - CLAUDE_CODE environment variable (auto-detect Claude Code)
+//
+// Agent mode provides ultra-compact output optimized for LLM context windows.
+func IsAgentMode() bool {
+	if os.Getenv("BD_AGENT_MODE") == "1" {
+		return true
+	}
+	// Auto-detect Claude Code environment
+	if os.Getenv("CLAUDE_CODE") != "" {
+		return true
+	}
+	return false
+}
+
 // Ayu theme color palette
 // Dark: https://terminalcolors.com/themes/ayu/dark/
 // Light: https://terminalcolors.com/themes/ayu/light/

internal/ui/styles_test.go

@@ -152,3 +152,26 @@ func TestRenderCommandAndCategoryAreUppercaseSafe(t *testing.T) {
 		t.Fatalf("command output missing text: %q", cmd)
 	}
 }
+
+func TestIsAgentMode(t *testing.T) {
+	// Test default (no env vars) - t.Setenv automatically restores after test
+	t.Setenv("BD_AGENT_MODE", "")
+	t.Setenv("CLAUDE_CODE", "")
+	if IsAgentMode() {
+		t.Fatal("expected false with no env vars")
+	}
+
+	// Test BD_AGENT_MODE=1
+	t.Setenv("BD_AGENT_MODE", "1")
+	t.Setenv("CLAUDE_CODE", "")
+	if !IsAgentMode() {
+		t.Fatal("expected true with BD_AGENT_MODE=1")
+	}
+
+	// Test CLAUDE_CODE auto-detection
+	t.Setenv("BD_AGENT_MODE", "")
+	t.Setenv("CLAUDE_CODE", "something")
+	if !IsAgentMode() {
+		t.Fatal("expected true with CLAUDE_CODE set")
+	}
+}