add(auth): personal access tokens, user impersonation and permission-aware write tools

[elcreator]

• auth.mode=pat (default): emcp_tokens table, Bearer endpoint at /{api_prefix}/{server} without sApi, self-service manager page (Tools -> MCP tokens), emcp:token:* commands
• ImpersonateManagerUser: API requests run as the token/JWT owner with their role, permissions, document groups and locks (mirrors UserLogin::writeSession, never persisted); the emcp permission is required in API mode too
• content read tools honour document groups and view_unpublished; content.get returns the body fields; model catalog reads need the permission of the matching manager screen
• evo.elements.list|get and evo.write.content.update|create|publish, evo.write.elements.save, evo.write.cache.clear, gated by manager permissions, enable_write_tools and the mcp:write scope; each writes a manager_log row
• ToolProvider / WritesSite / ToolRegistry: other extras contribute tools to a server handle at runtime or via mcp.servers[].extra_tools, with the same write gates
• JSON-RPC notifications and ping map to mcp:read (sent by MCP clients on connect)
• docker/ compose environment with a preinstalled site, token, smoke test and opt-in extras