Isolate compact Rust API navigation from underlying controls

[rmcdaniel]

Problem

On the generated Rust API reference at https://rust.durable-workflow.com/durable_workflow/, opening the hamburger navigation at compact widths places a fixed 200px sidebar over the document without isolating the underlying page. At 390x844, the search field and multiple underlying links/summary controls are partially or completely covered but remain part of the interactive surface; at 640x360, underlying source and summary controls are likewise unreachable. The open state also reports the fixed navigation overlapping primary content.

The current visual workflow captures only the default rustdoc state, so shared layout changes can publish without exercising this navigation state.

Acceptance criteria

• Opening compact rustdoc navigation presents one isolated navigation surface; underlying document controls are inert or fully covered and cannot compete for pointer or keyboard input.
• The menu toggle remains reachable, closes the navigation, and preserves usable focus behavior.
• Capture both closed and open navigation at mobile and compact-height widths, plus the default desktop and intermediate layouts.
• The deployed open states have no geometry.unreachable_controls, unintended floating-element overlap, horizontal overflow, clipping, console errors, request failures, or HTTP errors.
• Make the open-sidebar interaction a required visual-evidence state for generated-reference layout or navigation changes.

Delete when

Delete when the deployed generated Rust reference passes the full responsive state matrix, including opening and closing compact navigation, with clean reachability and interaction evidence.