ci: refactor and optimize GitHub Actions workflows (#146)

* ci: refactor and optimize GitHub Actions workflows\n\n- **Consolidate build processes (`build.yml`, `release.yml`)**: Merged the standalone `.zip` (linux-build) and `.deb` (deb-build) jobs into a single matrix job (`build-and-package` / `build-release`).
  This prevents compiling the Rust binaries twice per architecture, effectively cutting the build time in half and saving CI runner minutes.
    - **Parallelize and fix Flatpak deployment (`flatter.yml`)**:
      - Converted `x86_64` and `aarch64` flatpak jobs to run concurrently via a matrix strategy, removing the sequential bottleneck.
      - Resolved an issue where GitHub Pages would only host the `aarch64` repository. Introduced a new `prepare-repo` job that downloads the `.flatpak` bundles from both architectures, merges them into a
  single OSTree repository locally, signs it with GPG, and deploys the unified multi-arch repository to GitHub Pages.
      - Configured `flatter.yml` to automatically attach the offline `.flatpak` bundles to GitHub Releases when triggered by a release event.
    - **Toolchain and cleanup**: Switched hardcoded Rust toolchain version (`1.96.0`) to `stable` across all workflows to prevent manual bumps in the future. Simplified bash scripts and removed redundant
  dependency installation steps.

* Extract Copr trigger into a separate job: Copr build now starts immediately in parallel with GitHub Actions builds, eliminating unnecessary waiting time.

* use ubuntu 22.04 to build binaries instead of ubuntu-latest

* fix cache poisoning

* another attemp to fix cache poisoning

* disable cache in setup-rust-toolchain

* use ubuntu-latest

* optimize dependencies in debug profile

* remove --release flag from build.yml and CARGO env vars

* fix flatter names collision

* better flatter key changing

* auto formatting

* add auto updating cargo-sources for dependabot pull requests

* add groups to dependabot.yml

* add github-actions to dependabot

* add ppa deb repo

* add concurrency: gh-pages-deploy

.github/workflows/dependabot-flatpak.yml

@@ -0,0 +1,36 @@
+name: Dependabot Flatpak Cargo Sources
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened]
+    paths:
+      - "Cargo.lock"
+
+jobs:
+  update-cargo-sources:
+    if: github.actor == 'dependabot[bot]'
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write # Needed to push back to the branch
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+        with:
+          ref: ${{ github.head_ref }}
+
+      - name: Setup Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.x"
+
+      - name: Install dependencies
+        run: pip install aiohttp toml
+
+      - name: Generate cargo-sources.json
+        run: bash ./scripts/generate-sources.sh
+
+      - name: Commit and push changes
+        uses: stefanzweifel/git-auto-commit-action@v5
+        with:
+          commit_message: "chore(flatpak): automatically update cargo-sources.json"
+          file_pattern: "packages/flatpak/cargo-sources.json"