Enable errcheck linter and fix all production code warnings

- Enabled errcheck linter (previously disabled)
- Set tests: false in .golangci.yml to focus on production code
- Fixed 27 errcheck warnings using Go best practices:
  * Database resources: defer func() { _ = rows.Close() }()
  * Transaction rollbacks: defer func() { _ = tx.Rollback() }()
  * Best-effort closers: _ = store.Close(), _ = client.Close()
  * File writes: proper error checking on Close()
  * Interactive input: handle EOF gracefully
  * File ops: ignore ENOENT on os.Remove()
- All tests pass
- Closes bd-58

Amp-Thread-ID: https://ampcode.com/threads/T-57c9afd3-9adf-40c2-8be7-3e493d200361
Co-authored-by: Amp <amp@ampcode.com>

cmd/bd/main.go

@@ -587,7 +587,7 @@ func restartDaemonForVersionMismatch() bool {
 		cmd.Stdin = devNull
 		cmd.Stdout = devNull
 		cmd.Stderr = devNull
-		defer devNull.Close()
+		defer func() { _ = devNull.Close() }()
 	}
 
 	if err := cmd.Start(); err != nil {
@@ -637,7 +637,11 @@ func tryAutoStartDaemon(socketPath string) bool {
 	if !acquireStartLock(lockPath, socketPath) {
 		return false
 	}
-	defer os.Remove(lockPath)
+	defer func() {
+		if err := os.Remove(lockPath); err != nil && !os.IsNotExist(err) {
+			debugLog("failed to remove lock file: %v", err)
+		}
+	}()
 
 	if handleExistingSocket(socketPath) {
 		return true
@@ -777,7 +781,7 @@ func setupDaemonIO(cmd *exec.Cmd) {
 		cmd.Stdin = devNull
 		go func() {
 			time.Sleep(1 * time.Second)
-			devNull.Close()
+			_ = devNull.Close()
 		}()
 	}
 }