server: hand out the Android client this server syncs with (2726)

A self-hoster should not need an account on someone else's forge to get the app
for their own notes. The Fabled-Git instance is private — which is why
`install.sh` already cannot fetch for anyone but the operator — so a release page
is no use as a distribution point. The server holding the notes is something the
person already trusts and already reaches.

It also keeps the pair in step by construction. Client and server negotiate a
sync protocol version before linking, so a server that also serves the client
cannot hand out a phone it is unable to talk to.

**Two files, and both must be present**: `thoughtsync.apk` and a
`thoughtsync-android.json` sidecar carrying `{version_name, version_code, size,
sha256}`. The sidecar exists because an APK keeps its version in a binary AXML
manifest, which Python cannot read and which is not worth putting `aapt` on a
Quart server to reach. CI writes it beside the APK, where the values are already
known — including the digest, computed over the same bytes it uploads, so a
phone can tell a truncated download from a complete one before handing it to the
installer. Not a trust anchor; the signature is that.

**Under DATA_DIR, not baked into the image.** Baking charges ~55 MiB to every
self-hoster including everyone who never touches Android. `/var/thoughtsync` is
already the mounted volume that holds attachments, so a build dropped there
survives container recreation.

**Absence is an ordinary state, not an error.** No APK means the key is absent
from `/api/config` — absent rather than null, so a client testing for it cannot
confuse "this server has no client" with "this server predates the field" — the
web UI hides the card instead of offering a button that 404s, and the metadata
route answers 404. A server whose owner does not use Android is not misconfigured.

**A mismatched pair also counts as no client.** If the sidecar's recorded size
does not match the file on disk, the two did not arrive together; serving one
build while advertising another is worse than serving none, because the phone
would compare versions against a promise the bytes do not keep. That makes the
copy order in docs/android-distribution.md load-bearing, and it is written down
there: APK first, sidecar last.

**The version is public, the bytes are not.** An updater has to be able to ask
"is there something newer?" cheaply and before it has done anything; 55 MiB is
not for anyone who can reach the port. `login_required` already accepts either a
session cookie or a device bearer token, so the browser and a linked phone both
work with no second auth path.

The Android lane now publishes both files to the same rolling `dev` release the
desktop bundles use, reusing `publish-release.sh` — its nullglob asset list was
already built for several jobs in separate workspaces publishing to one release,
which is exactly this. Signed builds only: publishing an unsigned APK would offer
people something they cannot install over what they already have.

Nine tests, DB-free like the rest of the suite — this lane runs no Postgres, so
the advertisement is asserted through `advertisement()` rather than through
`/api/config`, whose other half needs a database. Both routes ARE exercised,
because neither opens a session.

.forgejo/workflows/android.yml

@@ -173,6 +173,41 @@ jobs:
           apksigner="$(ls /opt/android-sdk/build-tools/*/apksigner | head -1)"
           "$apksigner" verify --print-certs "app/build/outputs/apk/release/app-release.apk"
 
+      # Staged with a STABLE name plus the sidecar the server reads its version
+      # out of — an APK keeps that in a binary manifest Python cannot parse, and
+      # `aapt` is not on a Quart server. Computed here, where the real values are
+      # already known.
+      - name: Stage the client for distribution
+        if: steps.build.outputs.keystore != ''
+        run: |
+          mkdir -p dist
+          cp "app/build/outputs/apk/release/app-release.apk" dist/thoughtsync.apk
+          size="$(wc -c < dist/thoughtsync.apk | tr -d ' ')"
+          sha="$(sha256sum dist/thoughtsync.apk | cut -d' ' -f1)"
+          cat > dist/thoughtsync-android.json <<JSON
+          {
+            "version_name": "${{ steps.build.outputs.name }}",
+            "version_code": ${{ steps.build.outputs.code }},
+            "size": $size,
+            "sha256": "$sha"
+          }
+          JSON
+          cat dist/thoughtsync-android.json
+
+      # The rolling dev channel, same fixed-tag release the desktop bundles use.
+      # CI artifacts are per-run and auth-gated, so they are no use as a fetch
+      # target; a release asset has a permanent URL. Only ever a SIGNED build —
+      # publishing an unsigned APK would offer people something they cannot
+      # install over what they already have.
+      - name: Publish to the dev channel
+        if: github.ref == 'refs/heads/dev' && steps.build.outputs.keystore != ''
+        working-directory: .
+        env:
+          GITHUB_TOKEN: ${{ github.token }}
+          RELEASE_TAG: dev
+          RELEASE_PRERELEASE: "true"
+        run: bash desktop/packaging/publish-release.sh
+
       - name: Upload the APK
         # Mirrored action, never actions/upload-artifact. @v4+ throws
         # GHESNotSupportedError client-side on this hostname, and @v3 is worse —