fix: always use .card element screenshot, decouple from full_page flag

The previous adaptive fix only kicked in when screenshot_full_page=True.
When a user had full_page=False, the path fell through to page.screenshot()
which captures the fixed viewport (820x1200 CSS, 1640x2400 actual) — leaving
huge empty space for short posts and truncating long posts mid-content.

Drop the full_page gate. .card element screenshot is now the default path
regardless of config. The flag is only used as a fallback when the element
screenshot fails (e.g. .card not present in HTML).

This makes short and long posts render correctly for every config:
  - a3a7a0d (short, 47 views): 1640x2400 with empty gray -> 1520x698
  - 3e6e0454 (long, 555 views + images): 1640x2400 cut off -> 1520x2596 full

main.py

@@ -948,12 +948,13 @@ class LinuxDoPreviewPlugin(Star):
 
             page.wait_for_timeout(300)
 
-            # ── 自适应截图：优先对 .card 元素截图，避免全页导致的巨大空白 ──
-            # 元素截图按内容的实际边界拍，零空白；否则回退到全页模式。
+            # ── 自适应截图：总是优先对 .card 元素截图，按内容实际边界拍 ──
+            # 元素截图零空白、零截断，不受 viewport 高度限制。
+            # `screenshot_full_page` 仅作为后备回退：元素截图失败时才使用。
             card_locator = page.locator(".card")
             full_page = self.config.get("screenshot_full_page", True)
             try:
-                if full_page and card_locator.count() > 0:
+                if card_locator.count() > 0:
                     card_locator.first.screenshot(
                         path=str(save_path),
                         timeout=timeout_ms,