feat: Slim dictionary (#2583)

Co-authored-by: Ryan Hitchman <hitchmanr@gmail.com>
Co-authored-by: Kurtis Grant <kurtis.b.grant@gmail.com>
Co-authored-by: kemonine <kemonine@kemonine.info>
Co-authored-by: DustinHu <hu.dustin@gmail.com>
Co-authored-by: Justin Mitchell <justin@jmitch.com>

USER_GUIDE.md

@@ -263,6 +263,8 @@ The Settings screen allows you to configure the device's behavior. There are a f
   - "ON" - Vertical space will be added between paragraphs in Reading Mode
   - "OFF" - Paragraphs will not have vertical space added, but will have first-line indentation
 
+- **Dictionary**: Select the StarDict dictionary used for word lookups while reading, or "None" to disable lookups. *(Only shown when at least one dictionary folder exists under `/dictionaries/` on the SD card — see [docs/dictionary.md](docs/dictionary.md) for setup and usage.)*
+
 - **Text Anti-Aliasing**: Whether to show smooth grey edges (anti-aliasing) on text in reading mode. Note this slows down page turns slightly.
 
 - **Images**: Whether to display embedded images (JPG/PNG) found in EPUB files; options are "ON" (default) or "OFF".
@@ -282,6 +284,7 @@ The Settings screen allows you to configure the device's behavior. There are a f
 - **Long-press Menu**: Selects the function bound to holding the menu button (Confirm) while reading an EPUB. **Cycles through the available functions** each time the setting is selected — additional functions may be added in future releases, so this is not a binary on/off toggle. A short press of Confirm always opens the reader menu as normal:
   - "Bookmark" (default) - Hold Confirm (~0.4 second) to drop a bookmark at the current page.
   - "KOSync" - Hold Confirm (~1 second) to launch KOReader sync directly.
+  - "Dictionary" - Hold Confirm (~0.4 second) to start dictionary word selection on the current page (see [docs/dictionary.md](docs/dictionary.md)).
   - "Disabled" - Long-press is ignored; only short-press opens the reader menu.
 
 - **Short Power Button Click**: Controls the effect of a short click of the power button:
@@ -583,7 +586,7 @@ If the device goes to sleep or you close the book while viewing a footnote, the
 * **Return to Home:** Press the **Back** button to close the book and return to the **[Home](#31-home-screen)** screen.
 * **Return to Browse Files:** Press and hold the **Back** button to close the book and return to the **[Browse Files](#33-browse-files-screen)** screen.
 * **Reader Menu:** Press **Confirm** to open the **[Reader Menu](#5-reader-menu)**, which includes chapter navigation, reading options, and more.
-* **Long-press Confirm (configurable):** Holding **Confirm** runs the function chosen by the **Long-press Menu** setting in **[Controls Settings](#363-controls)** — "Bookmark" (default) drops a bookmark, "KOSync" launches KOReader Sync, "Disabled" does nothing. A short press always opens the Reader Menu.
+* **Long-press Confirm (configurable):** Holding **Confirm** runs the function chosen by the **Long-press Menu** setting in **[Controls Settings](#363-controls)** — "Bookmark" (default) drops a bookmark, "KOSync" launches KOReader Sync, "Dictionary" starts a word lookup, "Disabled" does nothing. A short press always opens the Reader Menu.
 
 ### Supported Languages
 
@@ -605,6 +608,7 @@ Available options include:
 
 - **Select Chapter** – Open the table of contents to jump to a specific chapter (see [Chapter Selection](#51-chapter-selection) below).
 - **Footnotes** – Navigate to the footnotes for the current section *(only shown in books that contain footnotes)*.
+- **Look Up** – Select a word on the current page and show its dictionary definition (see [docs/dictionary.md](docs/dictionary.md)). Requires a dictionary to be selected in **Settings → Reader → Dictionary**.
 - **Reading Orientation** – Cycle through screen orientations without leaving the reader.
 - **Auto Turn (Pages Per Minute)** – Cycle through automatic page turn speed options for hands-free reading.
 - **Go to %** – Jump to a specific position in the book by percentage.