Self-hosted APK distribution

Memby is handed out from a NAS or web server rather than a store, so:

- UpdateChecker gains a static-manifest source alongside Gitea. A .json
  update URL is read as a manifest ({version, apkUrl, notes}); anything
  else is still treated as a Gitea host. apkUrl may be relative and is
  resolved against the manifest's own URL.
- Release signing config reads memby.keystore from local.properties or
  the environment. Without it the build still succeeds but warns loudly:
  an unsigned APK will not install, and a changed key forces every user
  to uninstall before they can update.
- release.ps1 bumps the version, runs tests, builds a signed APK and
  assembles dist/out/ (landing page, latest.json, versioned APK) ready to
  copy onto the NAS.
- Keystores and dist/out are gitignored.

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

CLAUDE.md

@@ -71,7 +71,20 @@ authorities all derive from it.
 
 **Versioning.** `versionCode` is derived from `versionName`: `major*10000 + minor*100 +
 patch` (0.1.53 → 153). Bump both together — the in-app updater compares `versionName`,
-while Android refuses an APK whose `versionCode` went backwards.
+while Android refuses an APK whose `versionCode` went backwards. `release.ps1 -Version`
+rewrites both, so prefer it over editing the build file by hand.
+
+**Releases.** APKs are self-hosted (NAS or any web server), not on a store. `release.ps1`
+builds a signed APK and assembles `dist/out/` — `index.html` (landing page from
+`dist/template/`), `latest.json` (the manifest the app polls) and the versioned APK.
+Release signing reads `memby.keystore` and friends from `local.properties`; with no
+keystore the build still succeeds but emits an unsigned APK and logs a warning. The key
+matters more than the code: Android identifies an app by applicationId **plus** signing
+key, so a changed key forces every user to uninstall and reinstall.
+
+`UpdateChecker` supports two sources, chosen by URL shape in `isManifestUrl` — a `.json`
+URL is a static manifest, anything else is a Gitea host. `resolveApkUrl` lets a manifest
+use a relative `apkUrl`. Both are unit-tested in `UpdateSourceTest`.
 
 ## Architecture