feat(flatpak): add Flatpak packaging for universal distribution (#484)

* feat(flatpak): add Flatpak packaging for universal distribution

Adds a Flathub-ready Flatpak for the whisper.cpp engine, plus the minimal
runtime adaptations Flatpak actually needs — deliberately scoped down from the
earlier attempts (#416, #428), which bundled unrelated whisper.cpp GPU, audio,
and clipboard changes.

Packaging (packaging/flatpak/):
- app manifest, AppStream metainfo, and desktop entry (com.vocalinux.Vocalinux)
- generated offline Python dependency modules (flatpak-pip-generator)
- bundled shared modules: PortAudio, libayatana-appindicator, xdotool, xsel

Runtime changes (Flatpak-only, behaviour unchanged outside a sandbox):
- utils/paths.py: honour XDG_CONFIG_HOME/XDG_DATA_HOME so config, models and
  runtime data live under ~/.var/app/<app-id> in the sandbox
- autostart uses `flatpak run <app-id>` (the host launcher is always on PATH)
- text injection and keyboard backend detect a Wayland host reached via XWayland
  (no Wayland socket granted) and route through xdotool / pynput-on-X11
- tray indicator references the exported `<app-id>-*` host icon theme names

Also: a CI workflow building x86_64 + aarch64 bundles, and README / packaging
README / distro-compatibility doc updates.

Verified with a full flatpak-builder build + bundle install on aarch64:
pywhispercpp loads its native libraries without LD_LIBRARY_PATH, XDG paths
redirect correctly, bundled tools are present, and the entrypoint runs.
Manifest and builddir lint are clean and AppStream metadata validates.

Closes #167

* chore(flatpak): sync metainfo version to 0.14.0-beta

Also ignore flatpak-build-dir/ so local builder output stays untracked.

* refactor(flatpak): trim docs and comments after ponytail review

Drop redundant packaging README command blocks, shrink path/tray/autostart
comments, and stop ignoring a non-canonical build-dir name.

* fix(flatpak): close readiness gaps for v0.14.0-beta

Route log files through XDG data dirs so Flatpak keeps them under
~/.var/app, refresh AppStream screenshots to vocalinux.com, and use
the SPDX GPL-3.0-only license id.

* fix(flatpak): enable global hotkeys via evdev and --device=input

pynput over XWayland only receives keys for the focused X client. Prefer
evdev inside Flatpak and grant /dev/input so shortcuts work app-wide.

* fix(flatpak): inject text with ydotool/uinput on Wayland

xdotool only reaches XWayland clients, so typing appeared to succeed but
never hit native apps. Ship ydotool, grant --device=all for uinput, start
ydotoold on demand, and type via uinput inside the Flatpak.

* fix(flatpak): paste via wl-copy + Ctrl+V instead of typing

ydotool type injects character-by-character. Ship wl-clipboard, grant
--socket=wayland, and prefer clipboard paste for instant insertion.

* test(text-injection): expect ydotool default key-delay of 2

Matches the shipped VOCALINUX_YDOTOOL_KEY_DELAY default used when
clipboard paste falls back to character typing.

.github/workflows/flatpak.yml

@@ -0,0 +1,59 @@
+name: Flatpak
+
+on:
+  push:
+    branches: [ main, master ]
+    paths:
+      - 'packaging/flatpak/**'
+      - 'src/**'
+      - 'pyproject.toml'
+      - '.github/workflows/flatpak.yml'
+  pull_request:
+    branches: [ main, master ]
+    paths:
+      - 'packaging/flatpak/**'
+      - 'src/**'
+      - 'pyproject.toml'
+      - '.github/workflows/flatpak.yml'
+  workflow_dispatch:
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  build:
+    name: Build Flatpak (${{ matrix.arch }})
+    runs-on: ${{ matrix.runner }}
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - arch: x86_64
+            runner: ubuntu-latest
+          - arch: aarch64
+            runner: ubuntu-24.04-arm
+    container:
+      image: ghcr.io/flathub-infra/flatpak-github-actions:gnome-50
+      options: --privileged
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Build and bundle
+        uses: flatpak/flatpak-github-actions/flatpak-builder@v6
+        with:
+          bundle: vocalinux-${{ matrix.arch }}.flatpak
+          manifest-path: packaging/flatpak/com.vocalinux.Vocalinux.yml
+          cache-key: flatpak-${{ matrix.arch }}-${{ github.sha }}
+          arch: ${{ matrix.arch }}
+          # Flathub mirrors screenshots at submission time; mirror locally so the
+          # builddir linter does not flag the external screenshot URL.
+          mirror-screenshots-url: https://dl.flathub.org/media
+
+      - name: Upload bundle
+        uses: actions/upload-artifact@v4
+        with:
+          name: vocalinux-flatpak-${{ matrix.arch }}
+          path: vocalinux-${{ matrix.arch }}.flatpak
+          if-no-files-found: error