Correct sticky delay, unknown-key, and response-status documentation

[gravity-api]

Problem

The manifest never mentions HTTP/response-status behavior (no "status"/"exception"/"throw" match) despite the code calling response.EnsureSuccessStatusCode() (line 115), which throws on any non-2xx response. The Delay parameter description is scoped to "sequential (non-sticky) key sending," but the code always includes Delay in the request regardless of sticky mode — the documented scope isn't enforced client-side.

Proposed change

Update the manifest's description/parameter text to accurately reflect response-status behavior (throws on non-success) and the Delay parameter's actual scope (always sent, not sticky-conditional client-side) — do this after #81/#86 land so the documentation describes final behavior, not the current gap.

Compatibility requirements

1. Documentation-only; must describe actual post-fix behavior, not aspirational behavior.

Acceptance criteria

1. The manifest's description accurately reflects response-status handling and Delay's actual scope, cross-checked against the implementation after Reject negative and out-of-range User32 keyboard delays #79/Report incompatible User32 drivers instead of silently succeeding #81/Add cancellation and bounded timeouts to User32 keyboard dispatch #86.