Simplify calibration model, add pixel preview, and improve UI

- Replace segment-based calibration with core parameters (leds_top/right/bottom/left);
  segments are now derived at runtime via lookup tables
- Fix clockwise/counterclockwise edge traversal order for all 8 start_position/layout
  combinations (e.g. bottom_left+clockwise now correctly goes up-left first)
- Add pixel layout preview overlay with color-coded edges, LED index labels,
  direction arrows, and start position marker
- Move "Add New Device" form into a modal dialog triggered by "+" button
- Add display index selector to device settings modal
- Migrate from requirements.txt to pyproject.toml for dependency management
- Update Dockerfile and docs to use `pip install .`

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/Dockerfile

@@ -14,13 +14,11 @@ RUN apt-get update && apt-get install -y \
     libxcb-shape0 \
     && rm -rf /var/lib/apt/lists/*
 
-# Copy requirements and install Python dependencies
-COPY requirements.txt .
-RUN pip install --no-cache-dir -r requirements.txt
-
-# Copy application code
+# Copy project files and install Python dependencies
+COPY pyproject.toml .
 COPY src/ ./src/
 COPY config/ ./config/
+RUN pip install --no-cache-dir .
 
 # Create directories for data and logs
 RUN mkdir -p /app/data /app/logs