feat(outputs): physical monitor alignment, desktop overlay, coordinate simplification, and display identification

[ech678]

Overview

This PR adds physical monitor alignment, real-time desktop alignment overlay, coordinate normalization, and display identification to the Outputs page in nirimod.

Features & Enhancements

1. Physical Monitor Dimensions & Aspect-Ratio Scaling:

   • Supports millimeter dimensions from EDID with standard presets (24" 16:9, 27" 16:9, 32" 16:9, and Custom).
   • Canvas toggle (Physical vs Logical) to render monitors proportionally according to physical dimensions rather than raw pixel resolution, preventing visual distortion across mixed-DPI multi-monitor setups.

2. Real-Time Desktop Alignment Overlay (GtkLayerShell):

   • Lightweight overlay helper (alignment_overlay.py) using GtkLayerShell.
   • Click-through transparent overlay drawing a real-time horizontal laser alignment guide line with Vernier ruler ticks on screen edges.
   • Turns emerald green when displays achieve perfect center, top, or bottom alignment.
   • Fine-tune red line buttons (▲/▼ 1px and 10px) to directly compensate for physical desk mount height differences.
   • Canvas guide line toggle button in header.

3. Coordinate Simplification (Normalization):

   • Added Simplify button under Quick Alignment row to normalize multi-monitor bounding box origin to (0, 0).
   • Eliminates negative coordinate offsets while preserving exact relative distances between all displays.

4. Display Identification (Identify Displays):

   • Number badges (1, 2, ...) displayed on canvas monitor cards.
   • Identify button in header (find-location-symbolic) and suffix button on the Monitor selection row.
   • HUD card popup on each physical screen displaying large index numbers, connector names, model, resolution, refresh rate, and physical size with automatic 2.5s timeout.

5. Bugfixes & Robustness:

   • Prevent false dirty state on canvas clicks when outputs have not actually moved.
   • Stable overlay reference height anchoring across monitor selections.
   • 26 new comprehensive unit tests in tests/test_physical_outputs.py (118 repository tests passing).

[ech678]

Hi! Just a friendly heads-up: due to school and academic commitments, I might not be able to follow up or make modifications in a timely manner. Please feel free to review, adjust, or build upon any part of this PR as needed. Thank you for creating and maintaining nirimod!