feat: long-press Confirm launches KOReader sync from EPUB (#1808)

## Summary
- Hold the menu (Confirm) button for ≥1s while reading an EPUB to launch
the existing `KOReaderSyncActivity` directly — replaces the three-step
path (open reader menu → scroll to Sync → confirm) with a single
gesture.
- Reuses `ReaderUtils::GO_HOME_MS` (same 1s threshold used by long-press
Back) and the existing `KOREADER_STORE.hasCredentials()` guard.
- Adds a Controls picker **"Long-press Menu"** (`longPressMenuFunction`,
default **Bookmark**) that **cycles through the available functions**
bound to the long-press gesture: `KOSync → Disabled → Bookmark`. The
field name and `LONG_PRESS_MENU_FUNCTION` enum are intentionally general
so future actions (dictionary lookup, table of contents, etc.) can be
appended without another schema migration. The setting is **not** a
binary toggle.
- Existing menu Sync entry still works — both call sites share one
extracted helper (`launchKOReaderSync`); no logic duplication.
- Short-press Confirm release is gated on duration so the reader menu
does not also open after a long press that *acts*, mirroring the
existing long-press Back pattern.
- **No-credentials fall-through:** `launchKOReaderSync()` now returns
whether it acted. When the function is set to KOSync but no KOReader
credentials are stored, the long-press is a no-op that **falls through
to open the reader menu** — so the menu stays reachable instead of the
hold silently swallowing the gesture. The release is only suppressed
when sync actually launched or surfaced a save error.

## Test plan
- [x] `pio run` succeeds clean for the `default` ESP32-C3 environment.
- [x] On-device, value **KOSync**, valid KOReader credentials:
long-press Confirm ≥1s → sync screen launches; get + update progress
return HTTP 200; release does **not** also open the reader menu; returns
to the same page.
- [x] On-device, value **KOSync**, **no** credentials: long-press
Confirm falls through and **opens the reader menu** (regression fix);
short-press also opens the menu.
- [x] On-device: menu → Sync still launches the same screen (shared
helper) and syncs (200/200).
- [x] On-device, value **Bookmark**: long-press drops a bookmark and
does **not** also open the menu.
- [x] On-device, value **Disabled**: long-press Confirm opens the menu
on release; no sync, no bookmark.
- [x] On-device: long-press Back still goes to the file browser
(unchanged path).
- [x] Heap: epub is released before the TLS handshake (frees ~16 KB);
min free heap stayed ~84 KB during sync, well above the safe floor. No
panics/OOM across the session.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/activities/reader/EpubReaderActivity.h

@@ -60,6 +60,9 @@ class EpubReaderActivity final : public Activity {
   // Jump to a percentage of the book (0-100), mapping it to spine and page.
   void jumpToPercent(int percent);
   void onReaderMenuConfirm(EpubReaderMenuActivity::MenuAction action);
+  // Returns true if sync acted (launched, or surfaced a save error); false if it was a no-op
+  // because no KOReader credentials are stored.
+  bool launchKOReaderSync();
   void applyOrientation(uint8_t orientation);
   void toggleAutoPageTurn(uint8_t selectedPageTurnOption);
   void pageTurn(bool isForwardTurn);