feat: add branch_count to repository API (#35351) (#36743)

Description
This PR adds a branch_count field to the repository API response.
Currently, clients have to fetch all branches via /branches just to
determine the total number of branches. This addition brings Gitea
closer to parity with GitLab's API and improves efficiency for UI/CLI
clients that need this metric.

Linked Issue
Fixes #35351

Changes
API Structs: Added BranchCount field to Repository struct in
modules/structs/repo.go.

Database Logic: Implemented CountBranches in models/git/branch.go using
XORM for efficient counting.

Service Layer: Updated the ToRepo conversion logic in
services/convert/repository.go to populate the new field during API
serialisation.

Tests: Added a new unit test TestCountBranches in
models/git/branch_test.go to verify counts (including handling of
deleted branches).

Screenshots
<img width="196" height="121" alt="Screenshot 2026-02-24 at 21 41 07"
src="https://github.com/user-attachments/assets/cd023e92-f338-448b-9e49-0a5d54cc96c2"
/>

Testing
Manually verified the output using curl against a local Gitea instance.

Verified that adding a branch increments the count and deleting a branch
(soft-delete) decrements it.

Ran backend linting: make lint-backend (Passed).

Ran specific unit test: go test -v -tags "sqlite sqlite_unlock_notify"
./models/git -run TestCountBranches (Passed).

Co-authored-by: silverwind <me@silverwind.io>

models/git/branch.go

@@ -583,3 +583,12 @@ func FindRecentlyPushedNewBranches(ctx context.Context, doer *user_model.User, o
 
 	return newBranches, nil
 }
+
+// CountBranches returns the number of branches in the repository
+func CountBranches(ctx context.Context, repoID int64, includeDeleted bool) (int64, error) {
+	sess := db.GetEngine(ctx).Where("repo_id=?", repoID)
+	if !includeDeleted {
+		sess.And("is_deleted=?", false)
+	}
+	return sess.Count(new(Branch))
+}

models/git/branch_test.go

@@ -263,3 +263,25 @@ func TestOnlyGetDeletedBranchOnCorrectRepo(t *testing.T) {
 	assert.NoError(t, err)
 	assert.NotNil(t, deletedBranch)
 }
+
+func TestCountBranches(t *testing.T) {
+	// 1. Setup - Exactly like TestAddDeletedBranch
+	assert.NoError(t, unittest.PrepareTestDatabase())
+	repo := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: 1})
+
+	// 2. Execution - Using t.Context() to match the rest of the file
+	initialCount, err := git_model.CountBranches(t.Context(), repo.ID, false)
+	assert.NoError(t, err)
+
+	// 3. Database Action - Using t.Context()
+	err = db.Insert(t.Context(), &git_model.Branch{
+		RepoID: repo.ID,
+		Name:   "test-branch-for-counting",
+	})
+	assert.NoError(t, err)
+
+	// 4. Verification
+	newCount, err := git_model.CountBranches(t.Context(), repo.ID, false)
+	assert.NoError(t, err)
+	assert.Equal(t, initialCount+1, newCount)
+}