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>

routers/api/v1/repo/issue.go

@@ -47,9 +47,10 @@ func buildSearchIssuesRepoIDs(ctx *context.APIContext) (repoIDs []int64, allPubl
 		Actor:   ctx.Doer,
 	}
 	if ctx.IsSigned {
-		opts.Private = !ctx.PublicOnly
+		opts.Private = true
 		opts.AllLimited = true
 	}
+	opts.ApplyPublicOnly(ctx.PublicOnly)
 	if ctx.FormString("owner") != "" {
 		owner, err := user_model.GetUserByName(ctx, ctx.FormString("owner"))
 		if err != nil {