Add SyncPlay stats-for-nerds page, manual sync button, and release pipeline

Phase 0 scaffold plus everything since: quality negotiation, host-relay,
and active drift correction were each built and reverted after real bugs
in live use (see PLAN.md for the full account of each). What remains is
read-only SyncPlay observability (live drift/playback stats page) and a
one-shot manual "sync me to group" action, plus Phase 5 packaging/release
tooling (build.yaml, manifest.json generator, Gitea Actions release
workflow) to distribute it as a proper plugin repository.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

dev/plugins/JellyfinSyncPlus_0.1.0.0/meta.json

@@ -0,0 +1,13 @@
+{
+  "category": "General",
+  "name": "JellyfinSyncPlus",
+  "description": "Fixes SyncPlay drift via group quality negotiation, host-relay streaming, and active drift correction.",
+  "overview": "Fixes SyncPlay drift via group quality negotiation, host-relay streaming, and active drift correction.",
+  "owner": "cynic",
+  "version": "0.1.0.0",
+  "status": "Active",
+  "autoUpdate": false,
+  "targetAbi": "10.11.6.0",
+  "timestamp": "2026-07-09T00:00:00.0000000Z",
+  "guid": "267dbfe9-bb9c-4eeb-97aa-f0449283cfe6"
+}