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>

manifest.json

@@ -0,0 +1,20 @@
+[
+    {
+        "guid": "267dbfe9-bb9c-4eeb-97aa-f0449283cfe6",
+        "name": "JellyfinSyncPlus",
+        "description": "Read-only live view of every active SyncPlay group's members -- drift, position, play method, bitrate, and codec info -- plus a manual \"sync me to group\" button for one-shot self-correction. Does not touch playback automatically: earlier attempts at automatic quality-forcing and automatic drift correction both caused real problems in live use and were reverted (see PLAN.md). Reachable via Dashboard -> Plugins -> JellyfinSyncPlus.",
+        "overview": "SyncPlay stats for nerds: live drift/playback view plus a manual one-shot sync button.",
+        "owner": "cynic",
+        "category": "General",
+        "versions": [
+            {
+                "version": "0.2.0.0",
+                "changelog": "0.2.0.0: SyncPlay stats-for-nerds page and manual one-shot \"sync me to group\" button. No automatic playback intervention. 0.1.0.0: Phase 0 scaffold. Trivial plugin, no functionality yet.",
+                "targetAbi": "10.11.6.0",
+                "sourceUrl": "https://gitea.mrcynic.site/seer/JellyfinSyncPlus/releases/download/v0.2.0.0/JellyfinSyncPlus_0.2.0.0.zip",
+                "checksum": "4ff9b85a384bba6c246a46605e2be2e1",
+                "timestamp": "2026-07-09T15:05:04Z"
+            }
+        ]
+    }
+]