Feature/panorama

[skipperoo]

PR Description

• Added end-to-end Panorama stitching: new Panorama QML singleton, context-menu trigger in Library/Develop views, asynchronous stitching pipeline (OpenCV), and .pano.dng output with embedded thumbnail and DNG metadata.
• Reworked the tone processing pipeline across GPU preview (RawViewport.frag), CPU export (ImageDeveloper), and histogram generation (RawEngine) with sceneWhite normalization and Local Laplacian Filtering for highlights/shadows/whites/blacks + clarity behavior.
• Improved RAW decode defaults for preview/export (no_auto_bright = 0, auto_bright_thr = 0.01) and made source switching safer by resetting exposure/contrast through setters (plus a regression test for source switching behavior).
• Refined UI/UX: redesigned PhotoContextMenu, added Merge Photos submenu (Panorama active, HDR placeholder), wired panorama completion toast notifications, and stabilized Develop filmstrip refresh/filter behavior.
• Expanded build/release support: added OpenCV/TIFF dependencies in CMake and CI, introduced Linux/Windows Docker build scripts, improved Windows vcpkg cache handling, and updated AppImage packaging plugins.
• Standardized logging by migrating to typed LogLevel constants (PHOTON_*) and updated app settings wiring to use the new log-level API.