fix: Unify public-only token filtering in API queries and repo access checks (#37118) (#37773)

backport #37118 

This PR closes remaining `public-only` token gaps in the API by making
the restriction apply consistently across repository, organization,
activity, notification, and authenticated `/api/v1/user/...` routes.

Previously, `public-only` tokens were still able to:
- receive private results from some list/search/self endpoints,
- access repository data through ID-based lookups,
- and reach several authenticated self routes that should remain
unavailable for public-only access.

This change treats `public-only` as a cross-cutting visibility boundary:
- list/search endpoints now filter private resources consistently,
- repository lookups enforce the same restriction even when addressed
indirectly,
- and self routes that inherently expose or mutate private account state
now reject `public-only` tokens.

---
Generated by a coding agent with Codex 5.2

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>
Co-authored-by: Nicolas <bircni@icloud.com>

services/context/api.go

@@ -13,6 +13,7 @@ import (
 	"strconv"
 	"strings"
 
+	repo_model "code.gitea.io/gitea/models/repo"
 	"code.gitea.io/gitea/models/unit"
 	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/cache"
@@ -47,6 +48,12 @@ type APIContext struct {
 	PublicOnly bool // Whether the request is for a public endpoint
 }
 
+// TokenCanAccessRepo reports whether the current API token is allowed to access the repository.
+// A public-only token cannot reach a private repo; any other token is unrestricted by this check.
+func (ctx *APIContext) TokenCanAccessRepo(repo *repo_model.Repository) bool {
+	return repo == nil || !ctx.PublicOnly || !repo.IsPrivate
+}
+
 func init() {
 	web.RegisterResponseStatusProvider[*APIContext](func(req *http.Request) web_types.ResponseStatusProvider {
 		return req.Context().Value(apiContextKey).(*APIContext)