fetch: the fetch tool sets no tool annotations #5109

Problem

The fetch server's fetch tool sets no tool annotations, so tools/list reports no readOnlyHint, destructiveHint, idempotentHint or openWorldHint for it. Every tool in the git and time servers sets them, and AGENTS.md (MCP protocol) requires them on every tool that is added or changed; fetch was changed in this milestone (#1624, #4838). Clients use the hints to decide what to auto-approve.

Found by Copilot on the v1.0.0 merge PR #5090. Present on v2/main and v2/release/1.0.0.

Expected

fetch declares what it does: readOnlyHint: true (it only reads), destructiveHint: false, idempotentHint: true (repeating a request changes nothing on the server's side), openWorldHint: true (it reaches arbitrary hosts on the internet). A protocol test pins them.