everything: trigger-elicitation-request is listed for a client that supports only URL-mode elicitation #4985

Problem

trigger-elicitation-request sends a form-mode elicitation, but it is registered whenever the client declares the elicitation capability at all. A client that declares only URL-mode elicitation sees the tool listed, and every call to it fails.

Where it is pinned

src/everything/__tests__/sampling-elicitation.test.ts: "is listed for a URL-only client, which then cannot answer its form request", added in #4978 (Wave 1 of #4857). Each of these tests carries a KNOWN BUG marker: it asserts the current, wrong behavior, so the fix has to change it.

Expected

The tool is registered only when the client supports form-mode elicitation (or it adapts to the mode the client declared).

Done when

• The behavior above is fixed, in the legacy-era (2025-11-25) server on SDK 1.x.
• The pinning tests assert the correct behavior, and their KNOWN BUG markers are gone.
• The per-file 90% coverage gate still passes.