feat: implement dark mode theme and refactor viewer layout for improved responsiveness

CHANGELOG.md

@@ -20,6 +20,8 @@
 - Updated chat runtime image to include ffmpeg/ffprobe for media duration probing on upload.
 - Rebuilt viewer, admin, and admin-login pages around custom semantic class structures with accessibility-focused landmarks, tab semantics, and keyboard-focus behavior.
 - Replaced legacy and Tailwind-based stylesheet rules with a custom design-token CSS system covering responsive layouts, forms, tables, and reduced-motion behavior.
+- Switched the frontend theme to dark-mode-first token defaults with a light-scheme override path for users who prefer light appearance.
+- Refactored the viewer page to a single header plus unified content layout with responsive video/chat split, mobile stacking, and chat panel toggle behavior.
 - Code-split `hls.js` via lazy loading in the viewer bootstrap to shrink the main frontend bundle and isolate stream playback logic into a dedicated chunk.
 
 ### Fixed
@@ -30,6 +32,7 @@
 - Removed Tailwind and Alpine runtime/build dependencies from the frontend package configuration and eliminated Tailwind directives/warnings during production build.
 - Enforced 2GB upload ceiling plus server-side media file type/size validation for admin uploads.
 - Increased nginx `client_max_body_size` to allow resumable admin upload chunks and prevent `413 Content Too Large` responses.
+- Removed legacy now-playing viewer UI elements that conflicted with the streamlined single-header layout.
 
 ## [1.0.3] - 2026-08-03