fix(docs): copy section permalinks and polish outline navigation - #9972

Summary

• Copy the full section URL from heading permalinks, with success and failure feedback.
• Preserve native anchor navigation, browser history, and modified clicks.
• Dismiss the compact page outline with Escape and restore focus to its toggle.

Type of Change

• Bug fix

Testing

• Root lint, type-check, all repository audits, block registry check, and the full root test suite.
• Production docs build, HTTP acceptance checks, and the full docs corpus checks.
• Browser verification of mouse/keyboard copying, clipboard-unavailable recovery, new tabs, browser history, and compact outlines at phone and desktop widths in both themes.
• Chromium and WebKit browser acceptance suites, including permalink and outline regressions; clipboard readback verified in Chromium.

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing (new tests pass the test-audit authoring gate)
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)