feat(reader): swipe left/right to turn pages in single mode

Wire horizontal swipe into the mobile tap-zone overlay (single mode only,
so continuous mode keeps native vertical scroll). A leftward swipe past the
threshold turns to the next page, rightward to the previous; a mostly-
vertical drag is ignored so panning a tall page never turns it. The gesture
suppresses the synthesized zone tap so it doesn't double-fire. Swipe
classification is a pure, unit-tested helper; e2e drives real touch pointer
events for horizontal (both directions) and vertical cases.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "mangalord-frontend",
-  "version": "0.100.0",
+  "version": "0.101.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "mangalord-frontend",
-      "version": "0.100.0",
+      "version": "0.101.0",
       "devDependencies": {
         "@lucide/svelte": "^1.16.0",
         "@playwright/test": "^1.48.0",