update: bump 6 MCP packages + nixpkgs flake

- flake.lock: nixpkgs 2026-05-31 → 2026-06-16
- zotero-mcp: v0.2.2 → v0.5.0
- duckduckgo-mcp-server: 0.1.1-unstable → v0.4.0
- kindly-web-search-mcp-server: bump to latest commit + add trafilatura dep
- sabnzbd-mcp: pin to specific commit instead of refs/heads/main
- jellyfin-mcp: v2026.318.7 → v2026.604.2 (remove go.mod patch)
- nextcloud-mcp-server: v0.89.0 → v0.121.3

n8n-mcp, mcp-arr-server, pdf-reader-mcp held back:
upstream npm packages require @modelcontextprotocol/sdk versions
not yet published to npm registry

flake.lock

@@ -2,11 +2,11 @@
   "nodes": {
     "nixpkgs": {
       "locked": {
-        "lastModified": 1780243769,
-        "narHash": "sha256-x5UQuRsH3MqI0U9afaXSNqzTPSeZlRLvFAav2Ux1pNw=",
+        "lastModified": 1781577229,
+        "narHash": "sha256-lrp67w8AulE9Ks53n27I45ADSzbOCn4H+CNW1Ck8B+8=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "331800de5053fcebacf6813adb5db9c9dca22a0c",
+        "rev": "567a49d1913ce81ac6e9582e3553dd90a955875f",
         "type": "github"
       },
       "original": {