refactor: move remaining JSONL methods to models, clean up jsonl.py

- Add Tag.to_jsonl() method with schema_version
- Add Crawl.to_jsonl() method with schema_version
- Fix Tag.from_jsonl() to not depend on jsonl.py helper
- Update tests to use Snapshot.from_jsonl() instead of non-existent get_or_create_snapshot

Remove model-specific functions from misc/jsonl.py:
- tag_to_jsonl() - use Tag.to_jsonl() instead
- crawl_to_jsonl() - use Crawl.to_jsonl() instead
- get_or_create_tag() - use Tag.from_jsonl() instead
- process_jsonl_records() - use model from_jsonl() methods directly

jsonl.py now only contains generic I/O utilities:
- Type constants (TYPE_SNAPSHOT, etc.)
- parse_line(), read_stdin(), read_file(), read_args_or_stdin()
- write_record(), write_records()
- filter_by_type(), process_records()

archivebox/core/models.py

@@ -91,6 +91,19 @@ class Tag(ModelWithSerializers):
     def api_url(self) -> str:
         return reverse_lazy('api-1:get_tag', args=[self.id])
 
+    def to_jsonl(self) -> dict:
+        """
+        Convert Tag model instance to a JSONL record.
+        """
+        from archivebox.config import VERSION
+        return {
+            'type': 'Tag',
+            'schema_version': VERSION,
+            'id': str(self.id),
+            'name': self.name,
+            'slug': self.slug,
+        }
+
     @staticmethod
     def from_jsonl(record: Dict[str, Any], overrides: Dict[str, Any] = None):
         """
@@ -103,19 +116,18 @@ class Tag(ModelWithSerializers):
         Returns:
             Tag instance or None
         """
-        from archivebox.misc.jsonl import get_or_create_tag
-
-        try:
-            tag = get_or_create_tag(record)
-
-            # Auto-attach to snapshot if in overrides
-            if overrides and 'snapshot' in overrides and tag:
-                overrides['snapshot'].tags.add(tag)
-
-            return tag
-        except ValueError:
+        name = record.get('name')
+        if not name:
             return None
 
+        tag, _ = Tag.objects.get_or_create(name=name)
+
+        # Auto-attach to snapshot if in overrides
+        if overrides and 'snapshot' in overrides and tag:
+            overrides['snapshot'].tags.add(tag)
+
+        return tag
+
 
 class SnapshotTag(models.Model):
     id = models.AutoField(primary_key=True)