Give gem push a named credentials key

The push prompted for credentials and then died with "404 page not
found". Both are the same fault: RubyGems normalizes the keys in
~/.gem/credentials — dots become __ and a trailing slash is appended —
so a key written as the host URL can never match the --host value.
Finding no key, gem push falls back to signing in against the RubyGems
sign_in endpoint, which Gitea does not implement; that is the 404.

A named key is stored verbatim and is matched by --key, so the lookup
succeeds. Verified against Gem::ConfigFile with both formats.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.woodpecker.yaml

@@ -48,10 +48,15 @@ steps:
       - gem build warp_engine.gemspec
       - mkdir -p ~/.gem
       - TOKEN="$$(printf '%s' "$${FORGE_TOKEN}" | tr -d '[:space:]')"
+      # Nevesített kulcs, nem a hoszt-URL: a RubyGems a credentials fájl
+      # kulcsait normalizálja (a pontokból __ lesz, záró perjelet kap), így egy
+      # URL-kulcs sosem egyezik a --host értékével. Ilyenkor a gem push
+      # bejelentkezni próbál a RubyGems sign_in végpontján, amit a Gitea nem
+      # ismer — ez adta a "404 page not found"-ot.
       - |
-        printf -- '---\n:https://git.teletypegames.org/api/packages/engines/rubygems: Bearer %s\n' "$${TOKEN}" > ~/.gem/credentials
+        printf -- '---\n:gitea: Bearer %s\n' "$${TOKEN}" > ~/.gem/credentials
       - chmod 600 ~/.gem/credentials
-      - gem push --host https://git.teletypegames.org/api/packages/engines/rubygems warp_engine-*.gem
+      - gem push --key gitea --host https://git.teletypegames.org/api/packages/engines/rubygems warp_engine-*.gem
     when:
       - event: tag
         ref: refs/tags/warp_engine-v*