feat: an F-Droid repository at learn.halkyon.app

Releases also publish the APK in the project's own F-Droid repository,
https://learn.halkyon.app/fdroid/repo. tool/fdroid_repo.sh adds the APK,
signs the indexes with the repository's own key and uploads them to
ramiel as the user fdroid, whose key can only write into the folder
Caddy serves (rrsync), the APKs first and the indexes last.
tool/release.sh checks that key and its password before building and
publishes after the Forgejo release.

- tool/release/fdroid/ holds the repository's settings (Halkyon, the
  snap's icon) and the app's listing (the snap's text), with the
  anti-features TetheredNet (learn.halkyon.eu only, for now) and
  NonFreeNet (YouTube, the server's SSPL) declared with their reasons,
  in F-Droid's own definitions and with its icons (fdroiddata, AGPL v3).
- The index key's certificate is pinned: a new key would make the F-Droid
  app refuse the repository.
- fdroidserver v2.4.5, since Ubuntu's v2.2.1 knows neither TetheredNet
  nor reasons.

README and AGENTS.md describe it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

tool/release/fdroid-index-certificate.sha256

@@ -0,0 +1,5 @@
+# The SHA-256 of the certificate that signs the indexes of the F-Droid repository at
+# https://learn.halkyon.app/fdroid/repo (key alias halkyon-fdroid), as keytool prints it.
+# The F-Droid app knows the repository by it; tool/fdroid_repo.sh uploads no index
+# signed otherwise.
+E8:08:27:88:75:6F:6B:7E:68:2A:A2:2F:CE:AD:24:B5:3E:2A:8B:09:12:AD:66:D6:5E:8C:2D:4F:07:BB:94:B0

tool/release/fdroid/config.yml

@@ -0,0 +1,26 @@
+# The F-Droid repository at https://learn.halkyon.app/fdroid/repo, kept by
+# tool/fdroid_repo.sh: this folder is copied into the repository's working
+# folder (outside Git) before every update. Nothing secret is in here: the index
+# key's path and password come from the environment.
+repo_url: https://learn.halkyon.app/fdroid/repo
+archive_url: https://learn.halkyon.app/fdroid/archive
+repo_name: Halkyon
+repo_description: >-
+  Halkyon's apps, signed by their maintainer: the same APKs as on
+  code.halkyon.app.
+archive_name: Halkyon (archive)
+archive_description: >-
+  Older versions of Halkyon's apps.
+# The snap's icon, which tool/fdroid_repo.sh copies beside this file.
+repo_icon: halkyon.png
+archive_icon: halkyon.png
+# The newest three versions of each app stay in the repository, older ones move
+# to the archive.
+archive_older: 3
+
+keystore: $HALKYON_FDROID_KEYSTORE
+repo_keyalias: halkyon-fdroid
+# A PKCS #12 keystore has one password, for the store and its key.
+keystorepass: {env: HALKYON_FDROID_KEYSTORE_PASSWORD}
+keypass: {env: HALKYON_FDROID_KEYSTORE_PASSWORD}
+keydname: CN=Halkyon, O=Halkyon

tool/release/fdroid/config/antiFeatures.yml

@@ -0,0 +1,13 @@
+# The anti-features the repository's apps declare, as the main F-Droid
+# repository defines them: names, descriptions and icons from fdroiddata
+# (https://gitlab.com/fdroid/fdroiddata, config/antiFeatures.yml and the icons
+# beside it). The two icons are F-Droid's, under the GNU AGPL v3, fdroiddata's
+# licence. fdroid copies them into the repository's icons.
+NonFreeNet:
+  name: Non-Free Network Services
+  description: This app promotes or depends entirely on a non-free network service
+  icon: ic_antifeature_nonfreenet.png
+TetheredNet:
+  name: Tethered Network Services
+  description: This app depends entirely on a certain instance of a network service
+  icon: ic_antifeature_tetherednet.png

tool/release/fdroid/config/categories.yml

@@ -0,0 +1,3 @@
+# The categories the repository's apps are listed in.
+Education:
+  name: Education

tool/release/fdroid/metadata/app.halkyon.learn.yml

@@ -0,0 +1,25 @@
+# Halkyon Learn's listing in the F-Droid repository: the snap's summary and
+# description (snap/snapcraft.yaml), and its anti-features with their reasons.
+Categories:
+  - Education
+License: AGPL-3.0-or-later
+AuthorName: Halkyon
+AuthorEmail: support@halkyon.app
+WebSite: https://learn.halkyon.app
+SourceCode: https://code.halkyon.app/project-halkyon/halkyon_learn
+
+AntiFeatures:
+  TetheredNet: It connects to learn.halkyon.eu, the project's instance, and can't be
+    pointed at another one yet.
+  NonFreeNet: YouTube videos in study material play through YouTube, and the
+    server's licence (SSPL) isn't a free licence by F-Droid's definition.
+
+Name: Halkyon Learn
+Summary: Learn with flashcards, studied offline and synced between your devices
+Description: |-
+  Halkyon Learn is a spaced-repetition learning app: studysets of flashcards with
+  rich text, notes, learning paths and PDFs, reviewed on an FSRS schedule. It works
+  offline and syncs between your devices.
+
+  It starts with an anonymous account; signing in with GitHub later keeps
+  everything. It connects to learn.halkyon.eu, the project's instance.