ci(release): P1 hardening — versioning, F-Droid changelogs, R8 mapping, docs

P1.3 Versioning: the git tag is already the de-facto single source of truth
(every published versionCode uses MAJOR*10000+MINOR*100+PATCH; committed 13
was a stale outlier). Align the committed default to 20000 and document the
scheme in a comment + docs/RELEASING.md.

P1.4 F-Droid changelogs: a tag-only step extracts the tag's CHANGELOG section
into metadata/.../en-US/changelogs/<versionCode>.txt so clients show a
per-version "What's New". Also upload metadata/ (non-secret, never web-served)
alongside repo/ so changelog history survives across releases.

P1.5 R8 mapping: attach mapping-<version>.txt.gz to the Gitea release
(best-effort, continue-on-error) so user crash stacktraces stay
deobfuscatable. The gitea-release notes step is now an upsert (PATCH if the
release already exists) so it composes with the mapping step creating the
release first.

P1.6 docs/RELEASING.md: release ritual, versioning scheme, secrets inventory,
key custody/recovery, manual re-sign path, F-Droid repo details.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/RELEASING.md

@@ -0,0 +1,101 @@
+# Releasing Calendula
+
+Calendula is distributed through a self-hosted F-Droid repository. Every
+release is built, signed, and published automatically by
+`.gitea/workflows/release.yaml` when a version tag is pushed.
+
+## Versioning — the git tag is the single source of truth
+
+A release is defined by its tag, `vMAJOR.MINOR.PATCH` (e.g. `v2.1.0`). At
+release time the workflow derives both Gradle fields from the tag:
+
+- `versionName` = the tag without the leading `v` (`2.1.0`)
+- `versionCode` = `MAJOR*10000 + MINOR*100 + PATCH` (`2.1.0` → `20100`)
+
+So `MINOR` and `PATCH` each have room for 0–99. The values committed in
+`app/build.gradle.kts` are only the dev/local default — CI overwrites them
+from the tag. Keep the committed `versionCode`/`versionName` matching the
+**latest released tag** so local builds are sanely versioned; the published
+value always comes from the tag.
+
+Published version codes so far: `v0.1.0`→100 … `v1.0.0`→10000 … `v2.0.0`→20000.
+
+## Cutting a release
+
+1. Move the `## [Unreleased]` section of `CHANGELOG.md` under a new
+   `## [X.Y.Z] — <date>` heading (Keep a Changelog format). The text between
+   that heading and the next `## [` becomes both the Gitea release notes and
+   the F-Droid per-version changelog.
+2. Optionally bump the committed `versionCode`/`versionName` in
+   `app/build.gradle.kts` to match the new version (keeps local builds tidy).
+3. Commit, then tag and push:
+   ```bash
+   git tag vX.Y.Z
+   git push origin vX.Y.Z
+   ```
+4. The push triggers the release workflow. **Hold UI releases for on-device
+   review and explicit go-ahead before tagging.**
+
+## What the pipeline does
+
+`release.yaml` has three jobs:
+
+- **ci** — unit tests + a debug assemble (sanity).
+- **build-and-deploy** — derives the version, builds & signs the release APK
+  with the app key, copies it into the F-Droid repo, generates the per-version
+  changelog, re-signs the F-Droid index with the **repo key**, uploads
+  `repo/` + `metadata/` to the box, and attaches the R8 `mapping.txt` to the
+  Gitea release (best-effort).
+- **gitea-release** — creates/updates the Gitea release carrying the tag's
+  CHANGELOG section as notes. Gated on `ci` only (not the deploy) so notes
+  publish even if the F-Droid upload hiccups.
+
+### Manual re-sign / recovery
+
+A manual `workflow_dispatch` of the release workflow **from a branch** (not a
+tag) runs a **re-sign-only** path: it skips the APK build and just re-signs
+the existing F-Droid index with the configured repo key and re-uploads. Use
+this for key rotation or repo recovery without publishing a new app version.
+
+## Secrets (Gitea → repo Settings → Actions → Secrets)
+
+| Secret | Purpose |
+| --- | --- |
+| `KEYSTORE_BASE64`, `KEY_PASSWORD`, `KEY_ALIAS` | **App** signing key — signs the APK. Losing it means existing installs can't be updated. |
+| `FDROID_KEYSTORE_BASE64` | **F-Droid repo** signing key (`keystore.p12`, base64). Signs the repo index. |
+| `FDROID_CONFIG_BASE64` | F-Droid `config.yml` (base64) — repo metadata + keystore passwords. |
+| `HETZNER_HOST`, `HETZNER_USER`, `HETZNER_PASS` | Upload target for the F-Droid repo. |
+| `GITHUB_TOKEN` | Provided by Gitea Actions; used to create the release + attach assets. |
+
+The two keys are independent: the **app key** signs APKs; the **repo key**
+signs the index (its fingerprint is what users pin). Neither key nor the
+F-Droid `config.yml` is ever uploaded to the server — they live only in CI
+secrets and are reconstructed in-runner. If `FDROID_KEYSTORE_BASE64` /
+`FDROID_CONFIG_BASE64` are unset the workflow **fails loudly** rather than
+minting a new repo key (which would break every user's pinned fingerprint).
+
+## Key custody & recovery
+
+- **Offline backups** of both keys (and passwords) live in a password manager.
+  These are the only safe copies — losing them is unrecoverable.
+- **App key lost** → no existing install can be updated again; you'd have to
+  ship a new app under a new applicationId.
+- **Repo key lost or compromised** → rotate it, publish the new fingerprint in
+  the README, and have users remove + re-add the repo. To rotate: generate a
+  new `keystore.p12` + `config.yml`, set them as the `FDROID_*` secrets, update
+  the README fingerprint, and run the manual re-sign dispatch above.
+
+## F-Droid repo
+
+- URL: `https://apps.dev.jeanlucmakiola.de/dev/fdroid/repo`
+- Fingerprint (current): `C2C0640402BF458FC0ED957AF0B37AA4C14022E72F89CE90B5965B458CF73425`
+- Served from the Hetzner storage box. **nginx serves only `…/fdroid/repo/`** —
+  the working dir (key, config, metadata) sits above it and must never be
+  web-reachable. After any webserver change, verify `keystore.p12` and
+  `config.yml` return 404 while `repo/index-v2.json` returns 200.
+
+## Crash deobfuscation
+
+Each release attaches `mapping-<version>.txt.gz` (the R8 mapping) to its Gitea
+release. To deobfuscate a user stacktrace, download the mapping for that
+version and run it through `retrace`.