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/post.py

@@ -2,7 +2,12 @@
 
 import re
 from playwright.sync_api import expect
-from tests.conftest import BASE_URL, assert_share_copies, paste_image
+from tests.conftest import (
+    BASE_URL,
+    assert_share_copies,
+    create_post_with_files,
+    paste_image,
+)
 def create_post(page, topic="random", content="Test post content", title=None):
     page.goto(f"{BASE_URL}/feed", wait_until="domcontentloaded")
     page.locator(".feed-fab").first.wait_for(state="visible", timeout=10000)
@@ -13,6 +18,27 @@ def create_post(page, topic="random", content="Test post content", title=None):
         page.fill("#post-title", title)
     page.locator("#create-post-modal button.btn-primary:has-text('Post')").click()
     page.wait_for_url(f"{BASE_URL}/posts/*", wait_until="domcontentloaded")
+def _png_bytes(color=(0, 128, 255), size=(600, 400)):
+    import io
+    from PIL import Image
+
+    buf = io.BytesIO()
+    Image.new("RGB", size, color).save(buf, "PNG")
+    return buf.getvalue()
+
+
+def _gif_bytes():
+    import io
+    from PIL import Image
+
+    frames = [Image.new("RGB", (40, 40), c) for c in ((255, 0, 0), (0, 0, 255))]
+    buf = io.BytesIO()
+    frames[0].save(
+        buf, "GIF", save_all=True, append_images=frames[1:], duration=120, loop=0
+    )
+    return buf.getvalue()
+
+
 def _profile_stars(page, username):
     page.goto(f"{BASE_URL}/profile/{username}", wait_until="domcontentloaded")
     value = page.locator(
@@ -390,6 +416,57 @@ def test_paste_image_attaches_in_comment_form(alice):
     ).to_have_value(re.compile(r".+"))
 
 
+def test_single_image_post_shows_the_original_full_size(alice):
+    page, _ = alice
+    create_post_with_files(
+        page,
+        "Post carrying exactly one image",
+        [{"name": "shot.png", "mimeType": "image/png", "buffer": _png_bytes()}],
+    )
+    gallery = page.locator(".attachment-gallery.single")
+    gallery.wait_for(state="visible", timeout=10000)
+    img = gallery.locator(".gallery-thumb").first
+    src = img.get_attribute("src")
+    assert "_thumb" not in src, f"hero image served the 200px thumbnail: {src}"
+    assert src == img.get_attribute("data-full")
+
+
+def test_multiple_image_post_keeps_thumbnails(alice):
+    page, _ = alice
+    create_post_with_files(
+        page,
+        "Post carrying two images",
+        [
+            {"name": "one.png", "mimeType": "image/png", "buffer": _png_bytes()},
+            {
+                "name": "two.png",
+                "mimeType": "image/png",
+                "buffer": _png_bytes((200, 30, 90)),
+            },
+        ],
+        expected_count=2,
+    )
+    page.locator(".attachment-gallery").first.wait_for(state="visible", timeout=10000)
+    assert page.locator(".attachment-gallery.single").count() == 0
+    thumbs = page.locator(".attachment-gallery .gallery-thumb")
+    assert thumbs.count() == 2
+    for i in range(thumbs.count()):
+        assert "_thumb" in thumbs.nth(i).get_attribute("src")
+
+
+def test_animated_gif_post_serves_the_original_file(alice):
+    page, _ = alice
+    create_post_with_files(
+        page,
+        "Post carrying an animated gif",
+        [{"name": "loop.gif", "mimeType": "image/gif", "buffer": _gif_bytes()}],
+    )
+    img = page.locator(".attachment-gallery .gallery-thumb").first
+    img.wait_for(state="visible", timeout=10000)
+    src = img.get_attribute("src")
+    assert src.endswith(".gif"), f"animation lost, served {src}"
+
+
 def test_attachment_upload_ui(alice):
     import io
     from PIL import Image