Remove version field from metadata.json

- Removes noisy version mismatch warnings on every bd upgrade
- Version field in metadata.json was redundant with daemon version checking via RPC
- Daemon version mismatches still detected via HealthResponse
- Removes checkVersionMismatch() function and related test file
- Updates .beads/.gitignore to properly ignore merge artifacts

Amp-Thread-ID: https://ampcode.com/threads/T-7ba8aff2-97a0-4d0c-9008-e858bdfadd61
Co-authored-by: Amp <amp@ampcode.com>

internal/configfile/configfile.go

@@ -11,14 +11,12 @@ const ConfigFileName = "metadata.json"
 
 type Config struct {
 	Database     string `json:"database"`
-	Version      string `json:"version"`
 	JSONLExport  string `json:"jsonl_export,omitempty"`
 }
 
-func DefaultConfig(version string) *Config {
+func DefaultConfig() *Config {
 	return &Config{
 		Database:    "beads.db",
-		Version:     version,
 		JSONLExport: "beads.jsonl",
 	}
 }