feat(playlists): sentence-style two-way sync preview (only changed sides)

The confirm dialog spelled out both sides even when one was "+0 / −0", which read
as engineer shorthand. Build the message from one sentence per side that actually
changes and add a short "stays unchanged" line for the untouched side; the zero
side is no longer shown as a bare +0/−0 to decode. Assembled in the component
from granular i18n clauses (add/remove per side, reorder, rename) with count
plurals; HU+EN. Replaces the single pushPlanMerge template.

frontend/src/i18n/locales/en/playlists.json

@@ -35,7 +35,21 @@
   "pushTitle": "Sync to YouTube",
   "pushConfirm": "Sync",
   "pushPlanCreate": "Create a new YouTube playlist with {{count}} videos? (~{{units}} quota units; {{left}} left today.)",
-  "pushPlanMerge": "Two-way sync — on YouTube: +{{addYt}} / −{{removeYt}}; here: +{{addLocal}} / −{{removeLocal}}. (~{{units}} quota units; {{left}} left today.)",
+  "mergeAddLocal_one": "{{count}} video added to Siftlode from YouTube.",
+  "mergeAddLocal_other": "{{count}} videos added to Siftlode from YouTube.",
+  "mergeRemoveLocal_one": "{{count}} video removed from Siftlode.",
+  "mergeRemoveLocal_other": "{{count}} videos removed from Siftlode.",
+  "mergeAddYt_one": "{{count}} video added to YouTube.",
+  "mergeAddYt_other": "{{count}} videos added to YouTube.",
+  "mergeRemoveYt_one": "{{count}} video removed from YouTube.",
+  "mergeRemoveYt_other": "{{count}} videos removed from YouTube.",
+  "mergeReorder_one": "{{count}} video reordered on YouTube.",
+  "mergeReorder_other": "{{count}} videos reordered on YouTube.",
+  "mergeRename": "The playlist will be renamed on YouTube.",
+  "mergeYtUnchanged": "Your YouTube playlist stays unchanged.",
+  "mergeLocalUnchanged": "Your Siftlode playlist stays unchanged.",
+  "mergeQuota": " (~{{units}} quota units; {{left}} left today.)",
+  "mergeQuotaFree": " (~0 quota units.)",
   "pushNoQuota": "Not enough YouTube quota left today ({{left}}) for this sync (~{{units}} needed). Try again tomorrow.",
   "pushUpToDate": "“{{name}}” is already in sync with YouTube.",
   "pushDone": "“{{name}}” synced to YouTube ✓",

frontend/src/i18n/locales/hu/playlists.json

@@ -35,7 +35,21 @@
   "pushTitle": "Szinkron YouTube-ra",
   "pushConfirm": "Szinkron",
   "pushPlanCreate": "Létrehozol egy új YouTube-listát {{count}} videóval? (~{{units}} kvótaegység; ma még {{left}} maradt.)",
-  "pushPlanMerge": "Kétirányú szinkron — YouTube-on: +{{addYt}} / −{{removeYt}}; itt: +{{addLocal}} / −{{removeLocal}}. (~{{units}} kvótaegység; ma még {{left}} maradt.)",
+  "mergeAddLocal_one": "{{count}} videó bekerül a Siftlode-listádba a YouTube-ról.",
+  "mergeAddLocal_other": "{{count}} videó bekerül a Siftlode-listádba a YouTube-ról.",
+  "mergeRemoveLocal_one": "{{count}} videó törlődik a Siftlode-listádból.",
+  "mergeRemoveLocal_other": "{{count}} videó törlődik a Siftlode-listádból.",
+  "mergeAddYt_one": "{{count}} videó felkerül a YouTube-ra.",
+  "mergeAddYt_other": "{{count}} videó felkerül a YouTube-ra.",
+  "mergeRemoveYt_one": "{{count}} videó törlődik a YouTube-ról.",
+  "mergeRemoveYt_other": "{{count}} videó törlődik a YouTube-ról.",
+  "mergeReorder_one": "{{count}} videó átrendeződik a YouTube-on.",
+  "mergeReorder_other": "{{count}} videó átrendeződik a YouTube-on.",
+  "mergeRename": "A lista átnevezésre kerül a YouTube-on.",
+  "mergeYtUnchanged": "A YouTube-listád nem változik.",
+  "mergeLocalUnchanged": "A Siftlode-listád nem változik.",
+  "mergeQuota": " (~{{units}} kvótaegység; ma még {{left}} maradt.)",
+  "mergeQuotaFree": " (~0 kvótaegység.)",
   "pushNoQuota": "Nincs elég YouTube-kvóta mára ({{left}}) ehhez a szinkronhoz (~{{units}} kell). Próbáld újra holnap.",
   "pushUpToDate": "A(z) „{{name}}” már szinkronban van a YouTube-bal.",
   "pushDone": "„{{name}}” szinkronizálva a YouTube-ra ✓",