fix(ui): fix dashboard some style issues (#11461)

1.  Remove excess left and right margins
2. Remove excess bottom margin
3. Fixed the missing top rounded corner when repo is 0

| Before | After |
|----|----|
| ![Screenshot From 2026-02-26 04-02-03](/attachments/37da4f21-ae28-4708-a6be-a3421ebf5717) | ![Screenshot From 2026-02-26 04-01-39](/attachments/20cd29c4-0cb7-49ec-b7bb-99568364b4b7) |
| ![Screenshot From 2026-02-26 04-03-02](/attachments/d238275e-f231-4ae3-8de6-9418452ed6eb) | ![Screenshot From 2026-02-26 04-03-09](/attachments/eed862ef-b1db-46ac-aba0-9ac3089024c7) |
| ![image](/attachments/157bbc3e-2cdc-45c6-b4ca-236b3620f867) | ![Screenshot From 2026-03-01 19-50-41](/attachments/f22d963d-86d7-4c17-831a-307f990b1696) |

Co-authored-by: 0ko <0ko@noreply.codeberg.org>
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/11461
Reviewed-by: 0ko <0ko@noreply.codeberg.org>
Co-authored-by: panc <pan0xc@foxmail.com>
Co-committed-by: panc <pan0xc@foxmail.com>

web_src/css/dashboard.css

@@ -57,7 +57,7 @@
 
 .dashboard .dashboard-repos,
 .dashboard .dashboard-orgs {
-  margin: 0 1px; /* Accommodate for Semantic's 1px hacks on .attached elements */
+  margin-bottom: 0;
 }
 
 .dashboard .secondary-nav {