feat: donation banner, About tab, settings UI improvements

- Dismissible donation/open-source banner after 3+ sessions (30-day snooze)
- New About tab in Settings: version, repo link, license info
- Centralize project URLs (REPO_URL, DONATE_URL) in __init__.py, served via /health
- Center settings tab bar, reduce tab padding for 6-tab fit
- External URL save button: icon button instead of full-width text button
- Remove redundant settings footer close button
- Footer "Source Code" link replaced with "About" opening settings
- i18n keys for en/ru/zh

server/src/wled_controller/__init__.py

@@ -10,3 +10,9 @@ except PackageNotFoundError:
 
 __author__ = "Alexei Dolgolyov"
 __email__ = "dolgolyov.alexei@gmail.com"
+
+# ─── Project links ───────────────────────────────────────────
+GITEA_BASE_URL = "https://git.dolgolyov-family.by"
+GITEA_REPO = "alexei.dolgolyov/wled-screen-controller-mixed"
+REPO_URL = f"{GITEA_BASE_URL}/{GITEA_REPO}"
+DONATE_URL = ""  # TODO: set once donation platform is chosen