Add get_commit, get_repository_tree, and search_issues tools (#162)

Add three new read-only tools inspired by the GitHub MCP server:

- `get_commit`: Get details of a specific commit by SHA, branch, or tag
- `get_repository_tree`: Get the file tree of a repository with optional recursive traversal, pagination, and ref support
- `search_issues`: Search issues and pull requests across all accessible repositories with filters for state, type, labels, and owner

---------

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Reviewed-on: https://gitea.com/gitea/gitea-mcp/pulls/162
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-committed-by: silverwind <me@silverwind.io>

operation/repo/tree.go

@@ -0,0 +1,74 @@
+package repo
+
+import (
+	"context"
+	"fmt"
+
+	"gitea.com/gitea/gitea-mcp/pkg/gitea"
+	"gitea.com/gitea/gitea-mcp/pkg/log"
+	"gitea.com/gitea/gitea-mcp/pkg/params"
+	"gitea.com/gitea/gitea-mcp/pkg/to"
+
+	gitea_sdk "code.gitea.io/sdk/gitea"
+	"github.com/mark3labs/mcp-go/mcp"
+	"github.com/mark3labs/mcp-go/server"
+)
+
+const (
+	GetRepoTreeToolName = "get_repository_tree"
+)
+
+var GetRepoTreeTool = mcp.NewTool(
+	GetRepoTreeToolName,
+	mcp.WithDescription("Get the file tree of a repository"),
+	mcp.WithString("owner", mcp.Required(), mcp.Description("repository owner")),
+	mcp.WithString("repo", mcp.Required(), mcp.Description("repository name")),
+	mcp.WithString("tree_sha", mcp.Required(), mcp.Description("SHA, branch name, or tag name")),
+	mcp.WithBoolean("recursive", mcp.Description("whether to get the tree recursively")),
+	mcp.WithNumber("page", mcp.Description("page number"), mcp.DefaultNumber(1)),
+	mcp.WithNumber("perPage", mcp.Description("results per page"), mcp.DefaultNumber(30)),
+)
+
+func init() {
+	Tool.RegisterRead(server.ServerTool{
+		Tool:    GetRepoTreeTool,
+		Handler: GetRepoTreeFn,
+	})
+}
+
+func GetRepoTreeFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolResult, error) {
+	log.Debugf("Called GetRepoTreeFn")
+	args := req.GetArguments()
+	owner, err := params.GetString(args, "owner")
+	if err != nil {
+		return to.ErrorResult(err)
+	}
+	repo, err := params.GetString(args, "repo")
+	if err != nil {
+		return to.ErrorResult(err)
+	}
+	treeSHA, err := params.GetString(args, "tree_sha")
+	if err != nil {
+		return to.ErrorResult(err)
+	}
+	recursive, _ := args["recursive"].(bool)
+	page, pageSize := params.GetPagination(args, 30)
+
+	opt := gitea_sdk.ListTreeOptions{
+		ListOptions: gitea_sdk.ListOptions{
+			Page:     page,
+			PageSize: pageSize,
+		},
+		Ref:       treeSHA,
+		Recursive: recursive,
+	}
+	client, err := gitea.ClientFromContext(ctx)
+	if err != nil {
+		return to.ErrorResult(fmt.Errorf("get gitea client err: %v", err))
+	}
+	tree, _, err := client.GetTrees(owner, repo, opt)
+	if err != nil {
+		return to.ErrorResult(fmt.Errorf("get repository tree err: %v", err))
+	}
+	return to.TextResult(slimTree(tree))
+}