docs: refresh cache formats and web server workflows (#2233)

## Summary

* **What is the goal of this PR?** Update project documentation to match
the current master implementation for cache formats, i18n, file
transfer/web server workflows, SD-card fonts, and root user-facing docs.
* **What changes are included?** Refreshes `book.bin`/`section.bin` docs
for v6/v25, updates File Transfer/Calibre/WebDAV/API docs, documents 24
UI languages and JSON language persistence, updates root
README/USER_GUIDE cache and network details, and syncs the tracked
CLAUDE skill doc cache-version notes.

## Additional Context

* Docs-only change. Verified with `git diff --check origin/master..HEAD`
and stale-reference greps for old cache versions, removed i18n APIs, old
WiFi screen wording, and raw `Serial.printf` examples. No firmware build
was run.

---

### AI Usage

While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.

Did you use AI tools to help write this code? _**NO**_

docs/sd-card-fonts.md

@@ -9,15 +9,15 @@ There are three ways to install fonts:
 
 ### Option 1: Download from device (recommended)
 
-1. Connect your CrossPoint reader to WiFi
+1. Connect your CrossPoint reader to Wi-Fi
 2. Go to **Settings > System > Manage Fonts**
 3. Browse available font families and tap to download
 4. Downloaded fonts appear immediately in **Settings > Reader > Font Family**
 
 ### Option 2: Upload via web browser
 
-1. Connect your CrossPoint reader to WiFi
-2. Open the web interface in your browser (shown on the WiFi screen)
+1. Start **File Transfer** and connect through **Join Network** or **Create Hotspot**
+2. Open the web interface URL shown on the reader
 3. Navigate to the **Fonts** tab
 4. Upload `.cpfont` files using the upload form
 
@@ -96,6 +96,7 @@ To convert your own TrueType/OpenType fonts:
 | `latin-ext` | European languages (Latin + Extended-A/B + punctuation + ligatures) |
 | `greek` | Greek + Extended Greek |
 | `cyrillic` | Cyrillic + Supplement |
+| `hebrew` | Hebrew + Alphabetic Presentation Forms |
 | `georgian` | Georgian + Georgian Supplement |
 | `armenian` | Armenian |
 | `ethiopic` | Ethiopic + Extended |
@@ -107,7 +108,7 @@ To convert your own TrueType/OpenType fonts:
 | `tifinagh` | Tifinagh |
 | `symbols` | Math, currency, arrows, box-drawing, misc symbols, dingbats |
 | `reading` | Literary fiction coverage: Latin, Greek, Cyrillic, math/symbol blocks, supplemental punctuation, and CJK quote marks |
-| `builtin` | Matches built-in Bookerly coverage exactly |
+| `builtin` | Matches the firmware's built-in font conversion intervals |
 
 Combine presets with commas: `--intervals latin-ext,greek,cyrillic`
 
@@ -122,4 +123,4 @@ To list all presets with codepoint counts:
 
 `--force-autohint` — force FreeType's auto-hinter instead of the font's native hinting (useful when a font's built-in hints produce poor results at small sizes).
 
-Install custom fonts via WiFi upload or manual SD card copy.
+Install custom fonts via the web interface or manual SD card copy.