Add an Android uploader app

Native single-photo uploader for POST /upload. Lives in android/ with its
own flake, so the root flake stays Go-only and NixOS consumers of
nixosModules.default do not pull the Android SDK into their lock.

The server is untouched, so the app closes every gap client side:

- The slug is the enqueue-time timestamp, persisted in the work input.
  server.go derives the stored slug from the uploaded filename, so reusing
  that filename across WorkManager retries overwrites the same post rather
  than creating a duplicate. That stands in for an idempotency key.
- EXIF is stripped before upload. The gallery publishes the uploaded file
  verbatim as its full-size download, and phone photos carry GPS. JPEG and
  PNG drop metadata at marker and chunk level with the compressed pixels
  untouched; HEIC is decoded to JPEG because the extension check rejects it.
- Photos flagged for rotation are rotated into the pixels instead of relying
  on the orientation tag, which cannot survive the strip and which the
  thumbnailer ignores regardless.
- Anything over 18 MiB steps quality, then resolution, to stay inside
  nginx's client_max_body_size 20M.
- Credentials are sealed with an AES-GCM key in the Android Keystore. The
  key deliberately does not require user authentication, or background
  retries could not read it. Basic auth is attached by an interceptor
  rather than an Authenticator, which reacts to a 401 by replaying a
  multipart body that is not reliably replayable.
- The connection test uses GET /upload. /health is unreachable from outside
  because the nginx vhost only proxies location /upload.

WorkManager's SystemForegroundService needs foregroundServiceType declared
on the service entry, not just as a permission, or setForeground throws on
Android 14+. Only lintVitalRelease catches that, never a debug build.

Also anchors the .gitignore patterns. Unanchored, "photogallery" matched the
Kotlin package directory ws/inflo/photogallery/ and silently swallowed every
source file on git add.

.gitignore

@@ -1,8 +1,21 @@
-content/
-public/
-photogallery
-result
-result-*
+/content/
+/public/
+# Anchored: unanchored these would also match the Kotlin package directory
+# android/app/src/main/java/ws/inflo/photogallery/ and any nested "result".
+/photogallery
+/result
+/result-*
 *.tar.gz
 .envrc
 .direnv/
+
+# Android app
+android/.gradle/
+android/build/
+android/app/build/
+android/local.properties
+android/.idea/
+android/.kotlin/
+android/keystore.properties
+*.jks
+*.keystore