Document selection/hover highlight and fix README accuracy

- theme docs: selection-background-color controls border + hover
- README: fix ffmpeg mention, update library feature list

README.md

@@ -66,8 +66,8 @@ Supports custom styling via `custom.qss` — see [Theming](#theming).
 - Dedicated tab for browsing saved files on disk
 - Folder sidebar with configurable library directory
 - Sort by date, name, or size
-- FFmpeg-based video thumbnail generation
-- Missing file detection for removed or relocated media
+- Video thumbnail generation (ffmpeg if available, placeholder fallback)
+- Unreachable directory detection
 
 ### Search
 - Inline history dropdown inside the search bar

themes/README.md

@@ -28,7 +28,7 @@ QWidget {
     color: #ebdbb2;
     font-size: 13px;
     font-family: monospace;
-    selection-background-color: #fe8019;  /* also sets grid selection highlight */
+    selection-background-color: #fe8019;  /* grid selection border + hover highlight */
     selection-color: #282828;
 }
 ```
@@ -242,8 +242,9 @@ ThumbnailWidget {
 
 ## Notes
 
-- `selection-background-color` on `QWidget` controls the **grid thumbnail selection highlight**
+- `selection-background-color` on `QWidget` controls the **grid thumbnail selection border** and **hover highlight** (lighter version auto-derived)
 - Setting a custom QSS automatically switches to the Fusion Qt style for consistent rendering
 - Tag category colors (Artist, Character, etc.) in the info panel are set in code, not via QSS
 - Saved dot (green) and bookmark star (yellow) are QSS-controllable via `qproperty-savedColor` and `qproperty-bookmarkedColor` on `ThumbnailWidget`
 - Use `QLabel { background: transparent; }` to prevent labels from getting opaque backgrounds
+- Right-click on thumbnails selects visually but does not change the preview