feat(issue): add milestones and type filters to list_issues (#199)

## Summary

`list_issues` could not be scoped to a milestone, and the milestone was
absent from its list output. To find which milestone an issue belongs to,
callers had to read every issue individually — expensive on repositories
with hundreds of issues.

## Changes

- `list_issues`: add `milestones` (name or ID filter) and `type`
  (`issues`/`pulls`) parameters, wiring the SDK's
  `ListIssueOption.Milestones` and `ListIssueOption.Type`.
- Include the `milestone` `{id, title}` field in `slimIssues` (the list
  output), consistent with the existing `slimIssue` (single-issue) output.
- Tests: extend `Test_listRepoIssuesFn_filters` to assert the `milestones`
  and `type` query params, and add `Test_listRepoIssuesFn_includesMilestone`
  for the milestone field in list output.

This is a natural continuation of #164 (which added `labels`/`since`/`before`
to `list_issues`); `milestones` and `type` are supported by the SDK but were
not yet wired through.

## Testing

- `go build ./...` — ok
- `go vet ./operation/issue/` — ok
- `go test ./...` — all pass
- `make fmt` — clean

---
This PR was written with the help of Claude Opus 4.8

Reviewed-on: https://gitea.com/gitea/gitea-mcp/pulls/199
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: jermey <186737+jermey@noreply.gitea.com>
Co-committed-by: jermey <186737+jermey@noreply.gitea.com>

operation/issue/issue.go

@@ -44,7 +44,9 @@ var (
 		mcp.WithString("owner", mcp.Required(), mcp.Description(params.OwnerDesc)),
 		mcp.WithString("repo", mcp.Required(), mcp.Description(params.RepoDesc)),
 		mcp.WithString("state", mcp.DefaultString("all")),
+		mcp.WithString("type", mcp.Description("issues or pulls"), mcp.Enum("issues", "pulls")),
 		mcp.WithArray("labels", mcp.Description("label name filter"), mcp.Items(map[string]any{"type": "string"})),
+		mcp.WithArray("milestones", mcp.Description("milestone name or ID filter"), mcp.Items(map[string]any{"type": "string"})),
 		mcp.WithString("since", mcp.Description("updated after ISO 8601")),
 		mcp.WithString("before", mcp.Description("updated before ISO 8601")),
 		mcp.WithNumber("page", mcp.Description(params.PageDesc), mcp.DefaultNumber(1)),
@@ -181,15 +183,23 @@ func listRepoIssuesFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallTo
 		state = "all"
 	}
 	labels := params.GetStringSlice(req.GetArguments(), "labels")
+	milestones := params.GetStringSlice(req.GetArguments(), "milestones")
 	page, pageSize := params.GetPagination(req.GetArguments(), 30)
 	opt := gitea_sdk.ListIssueOption{
-		State:  gitea_sdk.StateType(state),
-		Labels: labels,
+		State:      gitea_sdk.StateType(state),
+		Labels:     labels,
+		Milestones: milestones,
 		ListOptions: gitea_sdk.ListOptions{
 			Page:     page,
 			PageSize: pageSize,
 		},
 	}
+	switch req.GetArguments()["type"] {
+	case "issues":
+		opt.Type = gitea_sdk.IssueTypeIssue
+	case "pulls":
+		opt.Type = gitea_sdk.IssueTypePull
+	}
 	if t := params.GetOptionalTime(req.GetArguments(), "since"); t != nil {
 		opt.Since = *t
 	}