Use git command instead of go git (#1005)

Remove go git library because it doesn't support sha256 repository but have an interface so that we could have other backend for the future.

Reviewed-on: https://gitea.com/gitea/tea/pulls/1005
Reviewed-by: Zettat123 <39446+zettat123@noreply.gitea.com>

modules/git/types.go

@@ -0,0 +1,163 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package git
+
+import (
+	"errors"
+	"strings"
+)
+
+var (
+	// ErrRepositoryNotExists indicates the requested path is not inside a git repository.
+	ErrRepositoryNotExists = errors.New("repository does not exist")
+	// ErrBranchExists indicates the requested branch already exists locally.
+	ErrBranchExists = errors.New("branch already exists")
+)
+
+// AuthMethod carries backend-agnostic authentication information for git operations.
+type AuthMethod struct {
+	Scheme        string
+	Username      string
+	Password      string
+	KeyFile       string
+	KeyPassphrase string
+}
+
+// CloneOptions describes repository clone behavior.
+type CloneOptions struct {
+	Depth    int
+	Insecure bool
+}
+
+// RepositoryBackend is the backend abstraction used by TeaRepo.
+type RepositoryBackend interface {
+	WorkTree() string
+	Config() (*Config, error)
+	Head() (*Reference, error)
+	AddRemote(name, remoteURL string) error
+	SetBranchUpstream(branchName, remoteName, remoteBranch string) error
+	Fetch(remoteName string, refspecs []string, auth *AuthMethod) error
+	CreateTrackingBranch(localBranchName, remoteBranchName, remoteName string) error
+	Checkout(ref ReferenceName) error
+	DeleteLocalBranch(branchName string) error
+	DeleteRemoteBranch(remoteName, remoteBranch string, auth *AuthMethod) error
+	ListReferences(prefixes ...string) ([]*Reference, error)
+	PushToAgitFlowPR(remoteName, head, base, topic string, pushOptions map[string]string, auth *AuthMethod) error
+}
+
+// Backend opens and clones repositories using a concrete git implementation.
+type Backend interface {
+	Name() string
+	Open(path string) (RepositoryBackend, error)
+	Clone(path, remoteURL string, auth *AuthMethod, opts CloneOptions) (RepositoryBackend, error)
+}
+
+// Config mirrors the repository config fields tea needs.
+type Config struct {
+	Remotes  map[string]*RemoteConfig
+	Branches map[string]*Branch
+}
+
+// RemoteConfig stores remote configuration.
+type RemoteConfig struct {
+	Name string
+	URLs []string
+}
+
+// Branch stores branch configuration.
+type Branch struct {
+	Name   string
+	Remote string
+	Merge  ReferenceName
+}
+
+// Validate checks whether the branch contains the fields tea needs.
+func (b *Branch) Validate() error {
+	if b == nil || b.Name == "" {
+		return errors.New("branch name is required")
+	}
+	return nil
+}
+
+// Remote wraps a configured git remote.
+type Remote struct {
+	repo   *TeaRepo
+	config *RemoteConfig
+}
+
+// Config returns the remote configuration.
+func (r *Remote) Config() *RemoteConfig {
+	if r == nil {
+		return nil
+	}
+	return r.config
+}
+
+// ReferenceName identifies a git reference.
+type ReferenceName string
+
+func (r ReferenceName) String() string { return string(r) }
+
+// Short returns the short display name for the reference.
+func (r ReferenceName) Short() string {
+	s := string(r)
+	switch {
+	case strings.HasPrefix(s, "refs/heads/"):
+		return strings.TrimPrefix(s, "refs/heads/")
+	case strings.HasPrefix(s, "refs/remotes/"):
+		return strings.TrimPrefix(s, "refs/remotes/")
+	case strings.HasPrefix(s, "refs/tags/"):
+		return strings.TrimPrefix(s, "refs/tags/")
+	default:
+		return s
+	}
+}
+
+// IsBranch reports whether the reference points to a local branch.
+func (r ReferenceName) IsBranch() bool {
+	return strings.HasPrefix(string(r), "refs/heads/")
+}
+
+// IsRemote reports whether the reference points to a remote-tracking branch.
+func (r ReferenceName) IsRemote() bool {
+	return strings.HasPrefix(string(r), "refs/remotes/")
+}
+
+// IsTag reports whether the reference points to a tag.
+func (r ReferenceName) IsTag() bool {
+	return strings.HasPrefix(string(r), "refs/tags/")
+}
+
+// Hash wraps a git object id.
+type Hash string
+
+func (h Hash) String() string { return string(h) }
+
+// Reference stores a resolved git ref and its hash.
+type Reference struct {
+	name ReferenceName
+	hash Hash
+}
+
+// Name returns the reference name.
+func (r *Reference) Name() ReferenceName { return r.name }
+
+// Hash returns the reference hash.
+func (r *Reference) Hash() Hash { return r.hash }
+
+// NewBranchReferenceName constructs a local branch ref name.
+func NewBranchReferenceName(name string) ReferenceName {
+	if strings.HasPrefix(name, "refs/") {
+		return ReferenceName(name)
+	}
+	return ReferenceName("refs/heads/" + name)
+}
+
+// NewRemoteReferenceName constructs a remote-tracking ref name.
+func NewRemoteReferenceName(remote, name string) ReferenceName {
+	if strings.HasPrefix(name, "refs/") {
+		return ReferenceName(name)
+	}
+	return ReferenceName("refs/remotes/" + remote + "/" + name)
+}