refactor: code cleanup across codebase (#947)

## Summary

- Extract duplicate \`getReleaseByTag\` into shared \`cmd/releases/utils.go\`
- Replace \`log.Fatal\` calls with proper error returns in config and login commands; \`GetLoginByToken\`/\`GetLoginsByHost\`/\`GetLoginByHost\` now return errors
- Remove dead \`portChan\` channel in \`modules/auth/oauth.go\`
- Fix YAML integer detection to use \`strconv.ParseInt\` (correctly handles negatives and large ints)
- Fix \`path.go\` error handling to use \`errors.As\` + \`syscall.ENOTDIR\` instead of string comparison
- Extract repeated credential helper key into local variable in \`SetupHelper\`
- Use existing \`isRemoteDeleted()\` in \`pull_clean.go\` instead of duplicating the logic
- Fix ~30 error message casing violations to follow Go conventions
- Use \`fmt.Errorf\` consistently instead of string concatenation in \`generic.go\`

Reviewed-on: https://gitea.com/gitea/tea/pulls/947
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Reviewed-by: Bo-Yi Wu (吳柏毅) <appleboy.tw@gmail.com>
Co-authored-by: Nicolas <bircni@icloud.com>
Co-committed-by: Nicolas <bircni@icloud.com>

cmd/flags/csvflag.go

@@ -44,7 +44,7 @@ func (f CsvFlag) GetValues(cmd *cli.Command) ([]string, error) {
 	if f.AvailableFields != nil && val != "" {
 		for _, field := range selection {
 			if !utils.Contains(f.AvailableFields, field) {
-				return nil, fmt.Errorf("Invalid field '%s'", field)
+				return nil, fmt.Errorf("invalid field '%s'", field)
 			}
 		}
 	}

cmd/flags/generic.go

@@ -5,6 +5,7 @@ package flags
 
 import (
 	"errors"
+	"fmt"
 
 	"code.gitea.io/sdk/gitea"
 	"github.com/urfave/cli/v3"
@@ -167,7 +168,7 @@ func ParseState(stateStr string) (gitea.StateType, error) {
 	case "closed":
 		return gitea.StateClosed, nil
 	default:
-		return "", errors.New("unknown state '" + stateStr + "'")
+		return "", fmt.Errorf("unknown state '%s'", stateStr)
 	}
 }
 
@@ -184,6 +185,6 @@ func ParseIssueKind(kindStr string, defaultKind gitea.IssueType) (gitea.IssueTyp
 	case "pull", "pulls", "pr":
 		return gitea.IssueTypePull, nil
 	default:
-		return "", errors.New("unknown kind '" + kindStr + "'")
+		return "", fmt.Errorf("unknown kind '%s'", kindStr)
 	}
 }

cmd/flags/issue_pr.go

@@ -165,7 +165,7 @@ func GetIssuePRCreateFlags(ctx *context.TeaContext) (*gitea.CreateIssueOption, e
 		}
 		ms, _, err := client.GetMilestoneByName(ctx.Owner, ctx.Repo, milestoneName)
 		if err != nil {
-			return nil, fmt.Errorf("Milestone '%s' not found", milestoneName)
+			return nil, fmt.Errorf("milestone '%s' not found", milestoneName)
 		}
 		opts.Milestone = ms.ID
 	}