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_test.go

@@ -63,10 +63,12 @@ func Test_listRepoIssuesFn_filters(t *testing.T) {
 	req := mcp.CallToolRequest{
 		Params: mcp.CallToolParams{
 			Arguments: map[string]any{
-				"owner":  owner,
-				"repo":   repo,
-				"labels": []any{"bug", "enhancement"},
-				"since":  "2026-01-01T00:00:00Z",
+				"owner":      owner,
+				"repo":       repo,
+				"type":       "issues",
+				"labels":     []any{"bug", "enhancement"},
+				"milestones": []any{"v1.0", "2"},
+				"since":      "2026-01-01T00:00:00Z",
 			},
 		},
 	}
@@ -85,6 +87,59 @@ func Test_listRepoIssuesFn_filters(t *testing.T) {
 	if !strings.Contains(gotQuery, "since=2026-01-01") {
 		t.Fatalf("expected since query param, got %s", gotQuery)
 	}
+	if !strings.Contains(gotQuery, "milestones=v1.0%2C2") {
+		t.Fatalf("expected milestones query param, got %s", gotQuery)
+	}
+	if !strings.Contains(gotQuery, "type=issues") {
+		t.Fatalf("expected type query param, got %s", gotQuery)
+	}
+}
+
+func Test_listRepoIssuesFn_includesMilestone(t *testing.T) {
+	const (
+		owner = "octo"
+		repo  = "demo"
+	)
+
+	handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		switch r.URL.Path {
+		case "/api/v1/version":
+			w.Header().Set("Content-Type", "application/json")
+			_, _ = w.Write([]byte(`{"version":"1.12.0"}`))
+		case fmt.Sprintf("/api/v1/repos/%s/%s", owner, repo):
+			w.Header().Set("Content-Type", "application/json")
+			_, _ = w.Write([]byte(`{"private":false}`))
+		case fmt.Sprintf("/api/v1/repos/%s/%s/issues", owner, repo):
+			w.Header().Set("Content-Type", "application/json")
+			_, _ = w.Write([]byte(`[
+				{"number": 1, "title": "with milestone", "state": "closed", "milestone": {"id": 5, "title": "v1.0"}},
+				{"number": 2, "title": "without milestone", "state": "open"}
+			]`))
+		default:
+			http.NotFound(w, r)
+		}
+	})
+	server := httptest.NewServer(handler)
+	defer server.Close()
+
+	origHost, origToken, origVersion := flag.Host, flag.Token, flag.Version
+	flag.Host, flag.Token, flag.Version = server.URL, "", "test"
+	defer func() { flag.Host, flag.Token, flag.Version = origHost, origToken, origVersion }()
+
+	req := mcp.CallToolRequest{Params: mcp.CallToolParams{Arguments: map[string]any{
+		"owner": owner, "repo": repo,
+	}}}
+	res, err := listRepoIssuesFn(context.Background(), req)
+	if err != nil {
+		t.Fatalf("listRepoIssuesFn() error = %v", err)
+	}
+	if res.IsError {
+		t.Fatalf("unexpected error result: %v", res.Content)
+	}
+	body := res.Content[0].(mcp.TextContent).Text
+	if !strings.Contains(body, `"milestone"`) || !strings.Contains(body, `"v1.0"`) {
+		t.Fatalf("expected milestone in list output, got: %s", body)
+	}
 }
 
 func Test_createIssueFn_labels(t *testing.T) {