Load heatmap data asynchronously (#36622)

Fixes: https://github.com/go-gitea/gitea/issues/21045

- Move heatmap data loading from synchronous server-side rendering to
async client-side fetch via dedicated JSON endpoints
- Dashboard and user profile pages no longer block on the expensive
heatmap DB query during HTML generation
- Use compact `[[timestamp,count]]` JSON format instead of
`[{"timestamp":N,"contributions":N}]` to reduce payload size
- Public API (`/api/v1/users/{username}/heatmap`) remains unchanged
- Heatmap rendering is unchanged, still shows a spinner as before, which
will now spin a litte bit longer.

Signed-off-by: silverwind <me@silverwind.io>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/web/user/heatmap.go

@@ -0,0 +1,66 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package user
+
+import (
+	"net/http"
+	"net/url"
+
+	activities_model "code.gitea.io/gitea/models/activities"
+	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/services/context"
+)
+
+func prepareHeatmapURL(ctx *context.Context) {
+	ctx.Data["EnableHeatmap"] = setting.Service.EnableUserHeatmap
+	if !setting.Service.EnableUserHeatmap {
+		return
+	}
+
+	if ctx.Org.Organization == nil {
+		// for individual user
+		ctx.Data["HeatmapURL"] = ctx.Doer.HomeLink() + "/-/heatmap"
+		return
+	}
+
+	// for org or team
+	heatmapURL := ctx.Org.Organization.OrganisationLink() + "/dashboard/-/heatmap"
+	if ctx.Org.Team != nil {
+		heatmapURL += "/" + url.PathEscape(ctx.Org.Team.LowerName)
+	}
+	ctx.Data["HeatmapURL"] = heatmapURL
+}
+
+func writeHeatmapJSON(ctx *context.Context, hdata []*activities_model.UserHeatmapData) {
+	data := make([][2]int64, len(hdata))
+	var total int64
+	for i, v := range hdata {
+		data[i] = [2]int64{int64(v.Timestamp), v.Contributions}
+		total += v.Contributions
+	}
+	ctx.JSON(http.StatusOK, map[string]any{
+		"heatmapData":        data,
+		"totalContributions": total,
+	})
+}
+
+// DashboardHeatmap returns heatmap data as JSON, for the individual user, organization or team dashboard.
+func DashboardHeatmap(ctx *context.Context) {
+	if !setting.Service.EnableUserHeatmap {
+		ctx.NotFound(nil)
+		return
+	}
+	var data []*activities_model.UserHeatmapData
+	var err error
+	if ctx.Org.Organization == nil {
+		data, err = activities_model.GetUserHeatmapDataByUser(ctx, ctx.ContextUser, ctx.Doer)
+	} else {
+		data, err = activities_model.GetUserHeatmapDataByOrgTeam(ctx, ctx.Org.Organization, ctx.Org.Team, ctx.Doer)
+	}
+	if err != nil {
+		ctx.ServerError("GetUserHeatmapData", err)
+		return
+	}
+	writeHeatmapJSON(ctx, data)
+}