Update dataset card

README.md

@@ -55,11 +55,13 @@ One row per publication reported in the project's final report.
 |---|---|---|
 | `url_id` | int | NCN `projekt_id` (foreign key → `ncn-projects`) |
 | `project_id` | str | Registration number |
-| `pub_type` | str | `article` or `book` |
+| `pub_type` | str | `article`, `book`, or `conference` |
+| `publication_id` | str | Internal deterministic publication key (`url_id:pub_type:title_norm`) |
 | `title` | str | Publication title |
 | `authors` | str | Author list |
 | `journal` | str | Journal or publisher name |
-| `doi` | str | DOI or URL (null if not reported) |
+| `doi` | str | Valid DOI identifier (null if not reported/invalid) |
+| `link` | str | Source publication URL (if reported) |
 | `quality_score` | float | Mock score: DOI present→1.0, absent→0.1, book→0.5 |
 
 > **Note:** `quality_score` is a placeholder. Real journal metrics (SJR, h-index)