feat(frontend): add keyboard shortcuts

[Harshitbro-ctrlv]

Description

Adds reusable and accessible keyboard shortcuts to the frontend:

• / focuses the code editor
• Ctrl/Cmd + Enter runs analysis
• Escape removes focus from the editor

Also adds visible shortcut hints, translations, ARIA metadata, documentation, and focused tests. Shortcuts do not interfere with unrelated input fields.

Related Issue

Fixes #1603

Type of change

• Bug fix
• New feature / enhancement
• Documentation update
• Test addition
• Refactor

Checklist

• I have read CONTRIBUTING.md
• My branch is up to date with main
• I have run pytest -v and all tests pass
• I have not introduced duplicate issues or features
• My PR title follows the format: feat/fix/docs/test: short description
• I have added tests for new features (Level 2 and 3 issues)
• No hardcoded secrets or API keys in my code
• This PR is linked to a GSSoC 2026 issue

Screenshots (if frontend change)

Test evidence

cd frontend/tests
npm test
# 2 test suites passed

cd ..
npm run test:static
# Passed

[github-actions]

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[Harshitbro-ctrlv]

Hi maintainers, this PR is still active and ready for review. The required workflows are awaiting maintainer approval. Please let me know if any changes are needed.

[github-actions]

👋 This PR has had no activity for 7 days.

Please push updates or comment if you still need more time.

Inactive PRs may be closed automatically after 7 more days.