Prepare common tmpl functions in a middleware (#33957)

Fix the TODO in `routers/web/web.go`, and avoid the unnecessary
`GetActiveStopwatch` SQL query in non-related route handlers.

routers/common/pagetmpl.go

@@ -0,0 +1,75 @@
+// Copyright 2025 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package common
+
+import (
+	goctx "context"
+	"errors"
+
+	activities_model "code.gitea.io/gitea/models/activities"
+	"code.gitea.io/gitea/models/db"
+	issues_model "code.gitea.io/gitea/models/issues"
+	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/services/context"
+)
+
+// StopwatchTmplInfo is a view on a stopwatch specifically for template rendering
+type StopwatchTmplInfo struct {
+	IssueLink  string
+	RepoSlug   string
+	IssueIndex int64
+	Seconds    int64
+}
+
+func getActiveStopwatch(goCtx goctx.Context) *StopwatchTmplInfo {
+	ctx := context.GetWebContext(goCtx)
+	if ctx.Doer == nil {
+		return nil
+	}
+
+	_, sw, issue, err := issues_model.HasUserStopwatch(ctx, ctx.Doer.ID)
+	if err != nil {
+		if !errors.Is(err, goctx.Canceled) {
+			log.Error("Unable to HasUserStopwatch for user:%-v: %v", ctx.Doer, err)
+		}
+		return nil
+	}
+
+	if sw == nil || sw.ID == 0 {
+		return nil
+	}
+
+	return &StopwatchTmplInfo{
+		issue.Link(),
+		issue.Repo.FullName(),
+		issue.Index,
+		sw.Seconds() + 1, // ensure time is never zero in ui
+	}
+}
+
+func notificationUnreadCount(goCtx goctx.Context) int64 {
+	ctx := context.GetWebContext(goCtx)
+	if ctx.Doer == nil {
+		return 0
+	}
+	count, err := db.Count[activities_model.Notification](ctx, activities_model.FindNotificationOptions{
+		UserID: ctx.Doer.ID,
+		Status: []activities_model.NotificationStatus{activities_model.NotificationStatusUnread},
+	})
+	if err != nil {
+		if !errors.Is(err, goctx.Canceled) {
+			log.Error("Unable to find notification for user:%-v: %v", ctx.Doer, err)
+		}
+		return 0
+	}
+	return count
+}
+
+func PageTmplFunctions(ctx *context.Context) {
+	if ctx.IsSigned {
+		// defer the function call to the last moment when the tmpl renders
+		ctx.Data["NotificationUnreadCount"] = notificationUnreadCount
+		ctx.Data["GetActiveStopwatch"] = getActiveStopwatch
+	}
+}