Show a post's image on its card, and show it full size

_attachment_display.html iterates a context variable named
`attachments`, so every caller binds it before the include.
_post_card.html was the one caller that did not: it guarded on
item.attachments but included the partial with nothing bound, so the
gallery looped over whatever `attachments` happened to be in the
surrounding page context and rendered empty. Every post with an image
looked image-less on the feed and on profiles, and on a project page -
where project_detail.html sets `attachments` at template scope for the
project's own files - a devlog card would have rendered the project's
files as its own.

With the image actually reaching the card, render a lone one properly:
a gallery holding exactly one item gets a `single` class and takes the
full content column (max-height 480px, object-fit contain, no hover
scale), matching the original DevPlace. That branch serves the stored
original rather than thumbnail_url, because a thumbnail is 200px on its
longest side and stretching it to the column width is visibly blurry.

Animated GIFs needed no change and now have a test proving it: they
never had a thumbnail to flatten, so they already took the original-file
path and simply render larger.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/e2e/feed.py

@@ -1,6 +1,6 @@
 # retoor <retoor@molodetz.nl>
 
-from tests.conftest import BASE_URL, paste_image
+from tests.conftest import BASE_URL, create_post_with_files, paste_image
 import time
 import requests
 from playwright.sync_api import expect
@@ -720,6 +720,28 @@ def test_paste_image_attaches_in_post_composer(alice):
     ).to_have_value(re.compile(r".+"))
 
 
+def test_feed_card_shows_the_post_image(alice):
+    import io
+    from PIL import Image
+
+    page, _ = alice
+    buf = io.BytesIO()
+    Image.new("RGB", (600, 400), (28, 120, 200)).save(buf, "PNG")
+    create_post_with_files(
+        page,
+        "Feed card image rendering check",
+        [{"name": "card.png", "mimeType": "image/png", "buffer": buf.getvalue()}],
+    )
+    page.goto(f"{BASE_URL}/feed", wait_until="domcontentloaded")
+    card = page.locator(
+        ".post-card:has-text('Feed card image rendering check')"
+    ).first
+    card.wait_for(state="visible", timeout=10000)
+    image = card.locator(".attachment-gallery.single .gallery-thumb").first
+    image.wait_for(state="visible", timeout=10000)
+    assert "_thumb" not in image.get_attribute("src")
+
+
 def test_create_post_cancel_modal(alice):
     page, _ = alice
     page.goto(f"{BASE_URL}/feed", wait_until="domcontentloaded")