Fix CodeQL code scanning alerts (#36858)

Fixes 10 CodeQL code scanning alerts:

- Change `NewPagination`/`SetLinkHeader` to accept `int64` for total
count, clamping internally to fix incorrect-integer-conversion alerts
([#110](https://github.com/go-gitea/gitea/security/code-scanning/110),
[#114](https://github.com/go-gitea/gitea/security/code-scanning/114),
[#115](https://github.com/go-gitea/gitea/security/code-scanning/115),
[#116](https://github.com/go-gitea/gitea/security/code-scanning/116))
- Use `strconv.Atoi()` in `htmlrenderer.go` to avoid int64 intermediate
([#105](https://github.com/go-gitea/gitea/security/code-scanning/105),
[#106](https://github.com/go-gitea/gitea/security/code-scanning/106))
- Clamp regex match indices in `escape_stream.go` to fix
allocation-size-overflow
([#161](https://github.com/go-gitea/gitea/security/code-scanning/161),
[#162](https://github.com/go-gitea/gitea/security/code-scanning/162),
[#163](https://github.com/go-gitea/gitea/security/code-scanning/163))
- Cap slice pre-allocation in `GetIssueDependencies`
([#181](https://github.com/go-gitea/gitea/security/code-scanning/181))

---------

Co-authored-by: Claude (Opus 4.6) <noreply@anthropic.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/indexer/code/search.go

@@ -130,7 +130,7 @@ func searchResult(result *internal.SearchResult, startIndex, endIndex int) (*Res
 }
 
 // PerformSearch perform a search on a repository
-func PerformSearch(ctx context.Context, opts *SearchOptions) (int, []*Result, []*SearchResultLanguages, error) {
+func PerformSearch(ctx context.Context, opts *SearchOptions) (int64, []*Result, []*SearchResultLanguages, error) {
 	if opts == nil || len(opts.Keyword) == 0 {
 		return 0, nil, nil, nil
 	}
@@ -149,5 +149,5 @@ func PerformSearch(ctx context.Context, opts *SearchOptions) (int, []*Result, []
 			return 0, nil, nil, err
 		}
 	}
-	return int(total), displayResults, resultLanguages, nil
+	return total, displayResults, resultLanguages, nil
 }