feat: add smart KOReader progress sync (#2192)

## Summary

Make KOReader progress sync a one-click flow for common cases while
keeping the existing manual mode available.

### Changes

- Add a **Sync Behavior** setting:
  - **Smart sync** for new configurations
  - **Ask every time** for manual control
- Preserve **Ask every time** when migrating an existing credential file
that predates this setting.
- In Smart mode:
  - upload local progress when no remote record exists;
  - show a short confirmation when already synced;
  - upload when local progress is further ahead;
  - apply remote progress when remote progress is further ahead.
- Probe both KOReader document-matching hashes before making the Smart
decision, while keeping uploads on the user's configured matching
method.
- Auto-return after successful Smart terminal states, with Back/Confirm
still available.
- Persist the setting alongside the current credential, matching-method,
and send-metadata fields.
- Document both behaviors in the user guide.

## Additional context

This pairs well with #2189 (smart Wi-Fi auto-connect), but does not
depend on it. It does not add background Wi-Fi or passive network
detection; sync is still triggered by the user from the reader menu.

Smart sync uses the furthest progress because CrossPoint does not
currently persist local progress timestamps. Users who prefer explicit
conflict resolution can select **Ask every time**.

## Verification

- `git diff --check`
- `platformio check --fail-on-defect low --fail-on-defect medium
--fail-on-defect high` — no defects
- `platformio run -e default` — firmware build successful
- The original implementation was manually smoke-tested on an X4 device.

---

### AI Usage

Did you use AI tools to help write this code? _**YES**_

AI tools were used to inspect the codebase, draft and review the
implementation, resolve the rebase against current `develop`, and
prepare the PR text. The resulting firmware was built locally.

---------

Co-authored-by: Alexander Hoffer <git@alexanderhoffer.com>
Co-authored-by: Alexander Hoffer <contact@alexanderhoffer.com>

USER_GUIDE.md

@@ -297,7 +297,7 @@ The Settings screen allows you to configure the device's behavior. There are a f
 
 - **Wi-Fi Networks**: Connect to Wi-Fi networks for file transfers and firmware updates.
 
-- **KOReader Sync**: Options for setting up KOReader for syncing book progress.
+- **KOReader Sync**: Options for setting up KOReader for syncing book progress. **Smart sync** is the default for new configurations and auto-resolves simple push/pull decisions. Existing credential files retain **Ask every time** when migrated; you can switch Sync Behavior at any time if you prefer manual confirmation.
 
 - **OPDS Servers**: Manage one or more OPDS [(Open Publication Distribution System)](https://en.wikipedia.org/wiki/Open_Publication_Distribution_System) libraries for browsing and downloading books. See [OPDS Servers (Multiple Libraries)](#365-opds-servers-multiple-libraries) below.
 
@@ -389,11 +389,10 @@ When this returns `HTTP 402` with `{"code":2002,"message":"Username is already r
    
    - Run **Authenticate**.
 
-3. While reading, press **Confirm** to open the reader menu, then select **Sync Progress**.
+3. While reading, press **Confirm** to open the reader menu, then select **Sync Progress**. Alternatively, set **Settings -> Controls -> Long-press Menu** to **KOSync** and hold Confirm to launch sync directly.
    
-   - Choose **Apply Remote** to jump to remote progress.
-   
-   - Choose **Upload Local** to push current progress.
+   - With **Sync Behavior** set to **Ask every time**, choose **Apply Remote** to jump to remote progress or **Upload Local** to push current progress.
+   - With **Sync Behavior** set to **Smart sync**, CrossPoint auto-resolves simple cases: upload when no remote progress exists, confirm and leave both unchanged when local and remote progress are already synchronized, upload when local progress is further ahead, or apply remote when remote progress is further ahead.
 
 ##### Option B: Self-Hosted Server (Docker Compose)
 
@@ -468,11 +467,10 @@ If this returns `HTTP 402` with `{"code":2002,"message":"Username is already reg
 
 If you use the HTTPS listener, use `https://<server-ip>:7200` (`curl -k` only for self-signed certificate testing).
 
-5. While reading, press **Confirm** to open the reader menu, then select **Sync Progress**.
+5. While reading, press **Confirm** to open the reader menu, then select **Sync Progress**. Alternatively, set **Settings -> Controls -> Long-press Menu** to **KOSync** and hold Confirm to launch sync directly.
    
-   - Choose **Apply Remote** to jump to remote progress.
-   
-   - Choose **Upload Local** to push current progress.
+   - With **Sync Behavior** set to **Ask every time**, choose **Apply Remote** to jump to remote progress or **Upload Local** to push current progress.
+   - With **Sync Behavior** set to **Smart sync**, CrossPoint auto-resolves simple cases: upload when no remote progress exists, confirm and leave both unchanged when local and remote progress are already synchronized, upload when local progress is further ahead, or apply remote when remote progress is further ahead.
 
 ### 3.7 Sleep Screen