[PORT] gitea##30237: Fix and rewrite contrast color calculation, fix project-related bugs

1. The previous color contrast calculation function was incorrect at
least for the `#84b6eb` where it output low-contrast white instead of
black. I've rewritten these functions now to accept hex colors and to
match GitHub's calculation and to output pure white/black for maximum
contrast. Before and after:
<img width="94" alt="Screenshot 2024-04-02 at 01 53 46"
src="00b39e15-a377-4458-95cf-ceec74b78228"><img
width="90" alt="Screenshot 2024-04-02 at 01 51 30"
src="1677067a-8d8f-47eb-82c0-76330deeb775">

2. Fix project-related issues:

- Expose the new `ContrastColor` function as template helper and use it
for project cards, replacing the previous JS solution which eliminates a
flash of wrong color on page load.
- Fix a bug where if editing a project title, the counter would get
lost.
- Move `rgbToHex` function to color utils.

Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: Giteabot <teabot@gitea.io>

---
Conflict resolution: Trivial.
(cherry picked from commit 36887ed3921d03f1864360c95bd2ecf853bfbe72)

web_src/css/features/projects.css

@@ -22,34 +22,27 @@
   cursor: default;
 }
 
+.project-column .issue-card {
+  color: var(--color-text);
+}
+
 .project-column-header {
   display: flex;
   align-items: center;
   justify-content: space-between;
 }
 
-.project-column-header.dark-label {
-  color: var(--color-project-board-dark-label) !important;
-}
-
-.project-column-header.dark-label .project-column-title {
-  color: var(--color-project-board-dark-label) !important;
-}
-
-.project-column-header.light-label {
-  color: var(--color-project-board-light-label) !important;
-}
-
-.project-column-header.light-label .project-column-title {
-  color: var(--color-project-board-light-label) !important;
-}
-
 .project-column-title {
   background: none !important;
   line-height: 1.25 !important;
   cursor: inherit;
 }
 
+.project-column-title,
+.project-column-issue-count {
+  color: inherit !important;
+}
+
 .project-column > .cards {
   flex: 1;
   display: flex;
@@ -64,6 +57,8 @@
 
 .project-column > .divider {
   margin: 5px 0;
+  border-color: currentcolor;
+  opacity: .5;
 }
 
 .project-column:first-child {

web_src/css/repo.css

@@ -2312,8 +2312,21 @@
   height: 0.5em;
 }
 
+.labels-list {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 0.25em;
+}
+
+.labels-list a {
+  display: flex;
+  text-decoration: none;
+}
+
 .labels-list .label {
-  margin: 2px 0;
+  padding: 0 6px;
+  margin: 0 !important;
+  min-height: 20px;
   display: inline-flex !important;
   line-height: 1.3; /* there is a `font-size: 1.25em` for inside emoji, so here the line-height needs to be larger slightly */
 }

web_src/css/repo/issue-list.css

@@ -69,23 +69,6 @@
   }
 }
 
-#issue-list .flex-item-title .labels-list {
-  display: flex;
-  flex-wrap: wrap;
-  gap: 0.25em;
-}
-
-#issue-list .flex-item-title .labels-list a {
-  display: flex;
-  text-decoration: none;
-}
-
-#issue-list .flex-item-title .labels-list .label {
-  padding: 0 6px;
-  margin: 0;
-  min-height: 20px;
-}
-
 #issue-list .flex-item-body .branches {
   display: inline-flex;
 }

web_src/css/themes/theme-gitea-dark.css

@@ -215,8 +215,6 @@
   --color-placeholder-text: var(--color-text-light-3);
   --color-editor-line-highlight: var(--color-primary-light-5);
   --color-project-board-bg: var(--color-secondary-light-2);
-  --color-project-board-dark-label: #0e1011;
-  --color-project-board-light-label: #dde0e2;
   --color-caret: var(--color-text); /* should ideally be --color-text-dark, see #15651 */
   --color-reaction-bg: #e8e8ff12;
   --color-reaction-hover-bg: var(--color-primary-light-4);

web_src/css/themes/theme-gitea-light.css

@@ -215,8 +215,6 @@
   --color-placeholder-text: var(--color-text-light-3);
   --color-editor-line-highlight: var(--color-primary-light-6);
   --color-project-board-bg: var(--color-secondary-light-4);
-  --color-project-board-dark-label: #0e1114;
-  --color-project-board-light-label: #eaeef2;
   --color-caret: var(--color-text-dark);
   --color-reaction-bg: #0000170a;
   --color-reaction-hover-bg: var(--color-primary-light-5);