Add per-user page tone modes to reader

README.md

@@ -127,6 +127,7 @@ whole-series completeness. See the scraper service and library format contracts
 - **Which mode opens:** Settings → *Open chapters in* = a fixed mode or *the mode I used last*. With *Use the fitting mode…* on, content that isn't made for your choice opens in the mode that fits (webtoons always open in Flow). That automatic switch never changes your remembered mode. Only clicking a mode in the reader does.
 - **Page zoom:** 100 % means the page fits the screen (in Flow: a normal single page fits the screen; for webtoons, the strip is as wide as the screen but never wider than its own width). Pages may end up larger than the screen, exactly fitting, or smaller. The toolbar −/+ buttons and keyboard `-`/`+` move in 5-percentage-point steps from 20 % through 600 %; `0` or the percentage button returns to 100 %. Ctrl + mouse wheel, touchpad pinch and two-finger pinch remain continuous for still finer control. This zooms only the pages; zooming over the toolbar zooms the whole page as usual. When a page is larger than the screen, drag it with the mouse (hand cursor) or pan with a finger. Flow locks horizontal movement while the content fits within the viewport, then enables it automatically when zoom makes the content wider. The zoom is remembered per mode for your account.
 - **Flow page gap:** Settings → Reading lets each user keep the normal separator between Flow pages or remove it for continuous webtoon artwork and text that crosses image edges.
+- **Page tone:** the reader's **Tone** button cycles Original → Inverted → Sepia → Dim → Extra dim in Flow, Page and Book. It changes only the artwork, never the controls or site theme. The choice is saved per user; it can also be selected in Settings → User → Reading.
 - **Active Reading Clock:** opt in under Settings → User → Reading time & privacy. No scrolling-speed limit; a visit counts at 60% viewed-page coverage and saves on exit. Pauses in the background or after 30 seconds without reader activity. Tap the clock for this visit's time, coverage, qualification and loading wait.
 - **Your Reading Story:** private active-time summaries appear on the library and manga pages when history exists. Chapter rows show the last timed read (60%-coverage visit), rereads remain visible as lifetime time, and Settings lets each user hide, export, or delete their own history. No leaderboards or speed ranking are used.
 - **Tap / click zones:**