refactor(ci): name the ISO workflows after their order and host, secrets for the mirror's URL and token

- iso-release.yml -> iso-1-github-tag.yml (ISO 1/2: tag and release, GitHub)
- steamify-iso.yml -> iso-2-gitea-build.yml (ISO 2/2: build and publish, Gitea)
- the mirror sync takes its URL and token from GIT_UPRISER_URL / GIT_UPRISER_TOKEN and retries
- docs and comments follow the new names

.github/workflows/build.yml

@@ -12,7 +12,7 @@ concurrency:
 jobs:
   build:
     # CachyOS's plain ISO and its quicktest matrix: only in CachyOS's own repo, not in this fork
-    # (the Steamify ISO is steamify-iso.yml).
+    # (the Steamify ISO is iso-2-gitea-build.yml).
     if: github.repository == 'CachyOS/CachyOS-Live-ISO'
     runs-on: ubuntu-latest
     container: