feat(tools): code_search (single-repo)

Adds SearchCode to gitea.Client and code_search MCP tool for single-repo
code search via GET /api/v1/repos/{owner}/{repo}/search?type=code.
Fan-out placeholder returns ErrValidation (lands in 7.3).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cmd/gitea-mcp/main.go

@@ -36,6 +36,7 @@ func main() {
 	reg.Register(tools.NewWorkflowRunTrigger(giteaClient, ownerAllow, cfg.GiteaBaseURL))
 	reg.Register(tools.NewWorkflowRunStatus(giteaClient, ownerAllow))
 	reg.Register(tools.NewRepoSearch(giteaClient, ownerAllow))
+	reg.Register(tools.NewCodeSearch(giteaClient, ownerAllow))
 
 	mcpSrv := mcp.NewServer(mcp.ServerOptions{
 		Registry: reg,