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/github.toml

@@ -0,0 +1,34 @@
+id = "github"
+name = "GitHub"
+description = "Access GitHub repositories, issues, pull requests, and organizations through the official MCP server"
+category = "devtools"
+icon = "🐙"
+tags = ["git", "vcs", "code", "issues", "pull-requests", "ci"]
+
+[transport]
+type = "stdio"
+command = "npx"
+args = ["-y", "@modelcontextprotocol/server-github"]
+
+[[required_env]]
+name = "GITHUB_PERSONAL_ACCESS_TOKEN"
+label = "GitHub Personal Access Token"
+help = "A fine-grained or classic PAT with repo and read:org scopes"
+is_secret = true
+get_url = "https://github.com/settings/tokens"
+
+[oauth]
+provider = "github"
+scopes = ["repo", "read:org"]
+auth_url = "https://github.com/login/oauth/authorize"
+token_url = "https://github.com/login/oauth/access_token"
+
+[health_check]
+interval_secs = 60
+unhealthy_threshold = 3
+
+setup_instructions = """
+1. Go to https://github.com/settings/tokens and create a Personal Access Token (classic or fine-grained) with 'repo' and 'read:org' scopes.
+2. Paste the token into the GITHUB_PERSONAL_ACCESS_TOKEN field above.
+3. Alternatively, use the OAuth flow to authorize LibreFang directly with your GitHub account.
+"""