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/gmail.toml

@@ -0,0 +1,27 @@
+id = "gmail"
+name = "Gmail"
+description = "Read, send, and manage Gmail messages and drafts through the Anthropic MCP server"
+category = "productivity"
+icon = "📧"
+tags = ["email", "google", "messaging", "inbox", "communication"]
+
+[transport]
+type = "stdio"
+command = "npx"
+args = ["-y", "@gongrzhe/server-gmail-autoauth-mcp"]
+
+[oauth]
+provider = "google"
+scopes = ["https://www.googleapis.com/auth/gmail.modify"]
+auth_url = "https://accounts.google.com/o/oauth2/v2/auth"
+token_url = "https://oauth2.googleapis.com/token"
+
+[health_check]
+interval_secs = 60
+unhealthy_threshold = 3
+
+setup_instructions = """
+1. Click 'Connect' to initiate the OAuth flow with your Google account.
+2. Grant LibreFang permission to read and modify your Gmail messages when prompted.
+3. The connection will be established automatically after authorization.
+"""