feat: sync content definitions from core repo

Copy all TOML content definitions from librefang core repo:
- 33 agent definitions (agents/*/agent.toml)
- 14 hand definitions with docs (hands/*/HAND.toml + SKILL.md)
- 25 integration templates (integrations/*.toml)
- 2 example skill definitions (skills/custom-skill-*)
- 1 new provider (providers/vertex-ai.toml)

Part of the framework-vs-content registry split (RFC v0.7).

integrations/mongodb.toml

@@ -0,0 +1,28 @@
+id = "mongodb"
+name = "MongoDB"
+description = "Query and manage MongoDB databases and collections through the MCP server"
+category = "data"
+icon = "🍃"
+tags = ["database", "nosql", "document", "mongo", "queries"]
+
+[transport]
+type = "stdio"
+command = "npx"
+args = ["-y", "@mongodb-js/mongodb-mcp-server"]
+
+[[required_env]]
+name = "MONGODB_URI"
+label = "MongoDB Connection URI"
+help = "A full MongoDB connection string (e.g., mongodb+srv://<user>:<password>@<cluster>.mongodb.net/<dbname>)"
+is_secret = true
+get_url = ""
+
+[health_check]
+interval_secs = 60
+unhealthy_threshold = 3
+
+setup_instructions = """
+1. Obtain your MongoDB connection URI from MongoDB Atlas (Clusters > Connect > Drivers) or your self-hosted instance.
+2. Ensure the database user has the necessary read/write permissions for the collections you want to access.
+3. Paste the full connection URI into the MONGODB_URI field above.
+"""