Add 'bd doctor' command to sanity check installation (#189)

* Add bd doctor command for installation health checks

Implements a comprehensive health check command similar to claude doctor
that validates beads installation and provides actionable recommendations.

Features:
- Installation check (.beads/ directory exists)
- Database version verification (compares with CLI version)
- ID format detection (hash-based vs sequential)
- CLI version check (fetches latest from GitHub)
- Storage type detection (SQLite vs JSONL-only mode)
- Tree-style output with color-coded warnings
- JSON output for scripting (--json flag)
- Actionable fix recommendations for each issue

Implementation improvements:
- Status constants instead of magic strings
- Semantic version comparison (fixes 0.10.0 vs 0.9.9 edge case)
- Documented defer pattern for intentional error ignore
- Comprehensive test coverage including version comparison edge cases
- Clean integration using slices.Contains for command list

Usage:
  bd doctor              # Check current directory
  bd doctor /path/to/repo # Check specific repository
  bd doctor --json       # Machine-readable output

* Simplify bd doctor documentation in README

Reduce verbose health check section to 2 lines as requested.

* Fix bd doctor to handle JSONL-only mode for ID format check

When no SQLite database exists (JSONL-only mode), skip the ID format
check instead of showing an error. This prevents the confusing
'Unable to query issues' error when the installation is actually fine.

cmd/bd/main.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"slices"
 	"strings"
 	"sync"
 	"time"
@@ -111,7 +112,8 @@ var rootCmd = &cobra.Command{
 		}
 
 		// Skip database initialization for commands that don't need a database
-		if cmd.Name() == "init" || cmd.Name() == cmdDaemon || cmd.Name() == "help" || cmd.Name() == "version" || cmd.Name() == "quickstart" {
+		noDbCommands := []string{"init", cmdDaemon, "help", "version", "quickstart", "doctor"}
+		if slices.Contains(noDbCommands, cmd.Name()) {
 			return
 		}