feat: Add built-in version tracking to bd (bd-loka)

Implement automatic bd version tracking and upgrade awareness:

- Add LastBdVersion field to Config struct in metadata.json
- Auto-update version on every bd command in PersistentPreRun
- Add 'bd upgrade' command with status/review/ack subcommands
- Show upgrade notifications on 'bd ready' and 'bd list'
- Non-intrusive: only shows once per session, skipped for JSON output

The system tracks version changes automatically and helps users stay
aware of bd upgrades without manual intervention. Notifications are
graceful - failures don't break commands.

Example output on bd ready after upgrade:
  🔄 bd upgraded from v0.22.0 to v0.24.2 since last use
  💡 Run 'bd upgrade review' to see what changed

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

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

internal/configfile/configfile.go

@@ -10,8 +10,9 @@ import (
 const ConfigFileName = "metadata.json"
 
 type Config struct {
-	Database     string `json:"database"`
-	JSONLExport  string `json:"jsonl_export,omitempty"`
+	Database      string `json:"database"`
+	JSONLExport   string `json:"jsonl_export,omitempty"`
+	LastBdVersion string `json:"last_bd_version,omitempty"`
 }
 
 func DefaultConfig() *Config {