chore: sync instance/dnspegasus with main, keeping instance manifests

Brings the aud-scope fix and README updates onto this branch. The three
manifest files are deliberately kept at this branch's instance-specific
values — a plain merge of main silently replaces them with the public
placeholders, which would break install from this branch.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

plugin/.mcp.json

@@ -2,9 +2,9 @@
   "mcpServers": {
     "shared-memory": {
       "type": "http",
-      "url": "https://memory.example.com/api/mcp",
+      "url": "https://memory.dnspegasus.net/api/mcp",
       "oauth": {
-        "clientId": "<OIDC_CLIENT_ID_MCP>",
+        "clientId": "5rkRS3rJhn3Ci9swWkxYMIrZ9OggsjOGy3cIOhYY",
         "callbackPort": 33418
       }
     }