Rework suggestion backend (#33538)

Fix #33522 

The suggestion backend logic now is

- If the keyword is empty, returned the latest 5 issues/prs with index
desc order
- If the keyword is digital, find all issues/prs which `index` has a
prefix with that, with index asc order
- If the keyword is non-digital or if the queried records less than 5,
searching issues/prs title with a `like`, with index desc order

## Empty keyword
<img width="310" alt="image"
src="https://github.com/user-attachments/assets/1912c634-0d98-4eeb-8542-d54240901f77"
/>

## Digital
<img width="479" alt="image"
src="https://github.com/user-attachments/assets/0356a936-7110-4a24-b21e-7400201bf9b8"
/>

## Digital and title contains the digital
<img width="363" alt="image"
src="https://github.com/user-attachments/assets/6e12f908-28fe-48de-8ccc-09cbeab024d4"
/>

## non-Digital
<img width="435" alt="image"
src="https://github.com/user-attachments/assets/2722bb53-baa2-4d67-a224-522a65f73856"
/>
<img width="477" alt="image"
src="https://github.com/user-attachments/assets/06708dd9-80d1-4a88-b32b-d29072dd1ba6"
/>

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/web/repo/issue_suggestions.go

@@ -6,13 +6,10 @@ package repo
 import (
 	"net/http"
 
-	"code.gitea.io/gitea/models/db"
-	issues_model "code.gitea.io/gitea/models/issues"
 	"code.gitea.io/gitea/models/unit"
-	issue_indexer "code.gitea.io/gitea/modules/indexer/issues"
 	"code.gitea.io/gitea/modules/optional"
-	"code.gitea.io/gitea/modules/structs"
 	"code.gitea.io/gitea/services/context"
+	issue_service "code.gitea.io/gitea/services/issue"
 )
 
 // IssueSuggestions returns a list of issue suggestions
@@ -29,54 +26,11 @@ func IssueSuggestions(ctx *context.Context) {
 		isPull = optional.Some(false)
 	}
 
-	searchOpt := &issue_indexer.SearchOptions{
-		Paginator: &db.ListOptions{
-			Page:     0,
-			PageSize: 5,
-		},
-		Keyword:  keyword,
-		RepoIDs:  []int64{ctx.Repo.Repository.ID},
-		IsPull:   isPull,
-		IsClosed: nil,
-		SortBy:   issue_indexer.SortByUpdatedDesc,
-	}
-
-	ids, _, err := issue_indexer.SearchIssues(ctx, searchOpt)
+	suggestions, err := issue_service.GetSuggestion(ctx, ctx.Repo.Repository, isPull, keyword)
 	if err != nil {
-		ctx.ServerError("SearchIssues", err)
+		ctx.ServerError("GetSuggestion", err)
 		return
 	}
-	issues, err := issues_model.GetIssuesByIDs(ctx, ids, true)
-	if err != nil {
-		ctx.ServerError("FindIssuesByIDs", err)
-		return
-	}
-
-	suggestions := make([]*structs.Issue, 0, len(issues))
-
-	for _, issue := range issues {
-		suggestion := &structs.Issue{
-			ID:    issue.ID,
-			Index: issue.Index,
-			Title: issue.Title,
-			State: issue.State(),
-		}
-
-		if issue.IsPull {
-			if err := issue.LoadPullRequest(ctx); err != nil {
-				ctx.ServerError("LoadPullRequest", err)
-				return
-			}
-			if issue.PullRequest != nil {
-				suggestion.PullRequest = &structs.PullRequestMeta{
-					HasMerged:        issue.PullRequest.HasMerged,
-					IsWorkInProgress: issue.PullRequest.IsWorkInProgress(ctx),
-				}
-			}
-		}
-
-		suggestions = append(suggestions, suggestion)
-	}
 
 	ctx.JSON(http.StatusOK, suggestions)
 }