feat(api): add project APIs (#38691)

Adds REST APIs for project boards for repo, org and user scopes, using
as much shared code as possible for all 3 scopes.

Fixes: https://github.com/go-gitea/gitea/issues/14299
Fixes: https://github.com/go-gitea/gitea/issues/31769
Fixes: https://github.com/go-gitea/gitea/issues/35921
Replaces: https://github.com/go-gitea/gitea/pull/37518
Replaces: https://github.com/go-gitea/gitea/pull/36008
Replaces: https://github.com/go-gitea/gitea/pull/28111
Replaces: https://github.com/go-gitea/gitea/pull/31768
Signed-off-by: silverwind <me@silverwind.io>
Co-authored-by: Supen.Huang <supen.huang@qq.com>
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Ember <ember@mubergacres.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: beardev-in <abhinav.edulakanti@gmail.com>

models/project/column_list_test.go

@@ -0,0 +1,40 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package project
+
+import (
+	"testing"
+
+	"gitea.dev/models/db"
+	"gitea.dev/models/unittest"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestGetColumnsPaginated(t *testing.T) {
+	assert.NoError(t, unittest.PrepareTestDatabase())
+
+	const projectID = 1
+	count, err := CountColumns(t.Context(), projectID)
+	assert.NoError(t, err)
+	assert.EqualValues(t, 3, count)
+
+	// Page 1, limit 2 — returns first 2 columns
+	page1, err := GetColumns(t.Context(), projectID, db.ListOptions{Page: 1, PageSize: 2})
+	assert.NoError(t, err)
+	assert.Len(t, page1, 2)
+
+	// Page 2, limit 2 — returns remaining column
+	page2, err := GetColumns(t.Context(), projectID, db.ListOptions{Page: 2, PageSize: 2})
+	assert.NoError(t, err)
+	assert.Len(t, page2, 1)
+
+	// Page 1 and page 2 together cover all columns with no overlap
+	allIDs := make(map[int64]bool)
+	for _, c := range append(page1, page2...) {
+		assert.False(t, allIDs[c.ID], "duplicate column ID %d across pages", c.ID)
+		allIDs[c.ID] = true
+	}
+	assert.Len(t, allIDs, 3)
+}