feat(update): unify the updater with Sabiá's Gitea-based mechanism

Replaces the signed tauri-plugin-updater (latest.json manifest, minisign
key pair) with the same simple mechanism Sabiá already uses: query the
Gitea Releases API directly, download the matching platform archive,
verify its SHA-256 checksum, and swap the binary in place. The CI job
that built the old latest.json manifest is removed in the next commit,
alongside an unrelated runner-routing change to the same workflow file.

- New guara-core::update module (check/apply), ported from
  sabia-core::update and adapted to Guará's own release asset naming
  (guara-<tag>-<platform>.tar.gz, matching scripts/package-cli.sh).
- New Engine::update_check / Engine::update_apply, wired into the RPC
  service for the browser UI.
- New CLI subcommand: "guara update" (check) and "guara update --apply"
  (download, verify, replace), mirroring "sabia update".
- GUI: replaced the Tauri plugin-updater flow (download_and_install,
  update-progress events, in-app restart) with a call to the new
  update_check/update_apply commands. The desktop app can no longer
  self-install in one click — it now points the user to the Releases
  page, same as Sabiá's desktop app already does.
- Removed tauri-plugin-updater, createUpdaterArtifacts and the
  updater.pubkey config, the signing-key loading in build-gui.sh, the
  CI step testing the old latest.json generator, and the now-unused
  make-latest-json.py/test_make_latest_json.py scripts.
- Documented the break for existing installs in CHANGELOG.md /
  CHANGELOG.pt-BR.md: versions up to 1.3.2 won't find this release
  automatically and need one manual download.

Trade-off accepted knowingly: SHA-256 verifies integrity against
Gitea's own API but, unlike the retired signed mechanism, does not
protect against a compromised Gitea server independently of it. This
is Lucas's own self-hosted instance, not a third-party mirror.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VAyr8d7HuAdUGB6aA5xmDD

CHANGELOG.md

@@ -4,6 +4,17 @@
 
 Format based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/); versions follow SemVer.
 
+## [1.3.3] - 2026-10-30
+
+Unified updater architecture with Sabiá: migrated from the signed `tauri-plugin-updater` to direct Gitea Releases API checking and self-updating with SHA-256 verification.
+
+### Changed
+- **New update mechanism:** The updater was rewritten to match Sabiá's model. Updates now query the Gitea Releases API directly, verify package checksums via `.sha256`, and no longer rely on `latest.json` or minisign updater keys.
+- **CLI self-update (`guara update`):** The CLI now supports `guara update` (checks for new versions) and `guara update --apply` (downloads, verifies SHA-256 checksum, and atomically replaces the binary).
+- **Desktop app notice:** The desktop app checks Gitea on startup and links directly to the new release packages.
+- **Important notice for existing installations:** Versions up to 1.3.2 used the previous signed `tauri-plugin-updater` mechanism looking for `latest.json`. Because that mechanism has been retired, existing installs will not automatically find version 1.3.3: download version 1.3.3 once manually from Gitea Releases, and future update checks will work through the new unified mechanism.
+- Removed `tauri-plugin-updater` dependency, `createUpdaterArtifacts` configuration, and the `updater` (`Build latest.json`) CI job.
+
 ## [1.3.2] - 2026-10-30
 
 The project moved from GitHub to Gitea, and the update check followed it.