ci: publish releases to Gitea instead of GitHub

The workflow was written for github.com: actions/upload-artifact failed on
the Gitea runner, softprops/action-gh-release only talks to the GitHub API,
and gen-manifest.js hardcoded github.com URLs.

- drop the artifact upload (release assets are the deliverable)
- upload release assets with tools/release-gitea.js, a dependency-free
  Gitea API client; re-running a tag replaces the attachments
- gen-manifest.js takes --server/PUBLIC_SERVER_URL and knows that Gitea
  spells the latest-asset URL /releases/download/latest/<file>
- PUBLIC_SERVER_URL is set explicitly because the runner only sees the
  instance's internal LAN address

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

README.md

@@ -54,12 +54,13 @@ settings from the backup it made.
 
 Add the repository once — *Homebrew Channel → Settings → Add repository*:
 
-```
-https://github.com/<owner>/<repo>/releases/latest/download/apps.json
+```text
+https://git.crylia.de/Crylia/lg_update_blocker/releases/download/latest/apps.json
 ```
 
-The app then shows up in the Homebrew Channel list, and every new release you
-tag is picked up automatically (that URL always points at the newest release).
+The app then shows up in the Homebrew Channel list, and every new release that
+is tagged is picked up automatically — Gitea resolves `.../download/latest/...`
+to the newest release.
 
 ### Manually
 
@@ -125,7 +126,8 @@ npm run deploy       # ares-install the resulting ipk
 
 ## Releasing
 
-`.github/workflows/release.yml` builds on every push. Tag a commit `v<version>`
+[.github/workflows/release.yml](.github/workflows/release.yml) builds on every
+push (Gitea Actions reads `.github/workflows/` too). Tag a commit `v<version>`
 (matching `version` in `package.json`) and the workflow additionally publishes a
 release containing:
 
@@ -135,6 +137,16 @@ release containing:
 * `apps.json` — the one-package repository index used by the repository URL above
 * `description.html` — the long description shown in the Homebrew Channel
 
+Uploading is done by [tools/release-gitea.js](tools/release-gitea.js) against
+the Gitea API (`softprops/action-gh-release` only speaks to github.com). It is
+idempotent: re-running a tag reuses the release and replaces the attachments.
+
+The URLs inside the manifest come from `PUBLIC_SERVER_URL` in the workflow, not
+from `GITHUB_SERVER_URL` — the runner is handed the instance's internal LAN
+address, which the TV cannot reach. Change that one variable if the instance
+moves. Generating for github.com instead works too: `--server` (or
+`PUBLIC_SERVER_URL`) switches the "latest release asset" URL to GitHub's shape.
+
 The app id lives in exactly one place: the `name` field of `package.json`.
 Change it there and everything (appinfo, service name, Luna URIs, manifest)
 follows.