feat: initial Dropbox tag sync tool

Cross-platform CLI that mirrors Dropbox web tags to OS-native tags:
- macOS: Finder xattrs (content-preserving, no re-upload)
- Windows: XMP:Subject via ExifTool (re-upload expected once per file)

Includes an interactive wizard that auto-detects the OS and Dropbox
folder, walks the user through read-only token creation, previews
tagged files, applies tags, and installs a background scheduler
(launchd on macOS, Task Scheduler on Windows).

Ships with:
- 47-test suite (pytest) covering config, state DB, run_sync, writers
- Gitea Actions CI for Linux / macOS / Windows with coverage reporting

.gitea/workflows/ci.yml

@@ -0,0 +1,95 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  test-linux:
+    name: Tests (Linux, Python ${{ matrix.python-version }})
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        python-version: ["3.9", "3.11", "3.12"]
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python-version }}
+          cache: pip
+          cache-dependency-path: |
+            requirements.txt
+            requirements-dev.txt
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install -r requirements-dev.txt
+
+      - name: Syntax check
+        run: |
+          python -m py_compile tagsync.py
+          python -c "import pathlib, py_compile; [py_compile.compile(str(p), doraise=True) for p in pathlib.Path('tagsync').rglob('*.py')]"
+
+      - name: CLI smoke test
+        run: |
+          python tagsync.py --help
+          python tagsync.py status
+
+      - name: Run tests with coverage
+        run: |
+          pytest --cov=tagsync --cov-report=term-missing --cov-report=xml
+
+      - name: Upload coverage artifact
+        if: matrix.python-version == '3.12'
+        uses: actions/upload-artifact@v3
+        with:
+          name: coverage-xml
+          path: coverage.xml
+          retention-days: 14
+
+  test-macos:
+    name: Tests (macOS)
+    runs-on: macos-latest
+    # macOS runners are more expensive — only run on main-branch pushes
+    # and PRs that touch platform_macos.py or core logic.
+    if: github.event_name == 'push' || contains(github.event.pull_request.labels.*.name, 'platform')
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+
+      - name: Install dependencies
+        run: pip install -r requirements-dev.txt
+
+      - name: Run tests
+        run: pytest -v
+
+  test-windows:
+    name: Tests (Windows)
+    runs-on: windows-latest
+    if: github.event_name == 'push' || contains(github.event.pull_request.labels.*.name, 'platform')
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+
+      - name: Install dependencies
+        run: pip install -r requirements-dev.txt
+
+      - name: Run tests
+        run: pytest -v