Activate the file upload button on Space and NumpadEnter

[rmuratov]

Closes #31

Problem

The "Choose files" label acts as a button but its keydown handler only checked event.code === 'Enter'. Real buttons also activate on Space, and NumpadEnter has a different code, so both were ignored.

Fix

The handler now checks event.key === 'Enter' || event.key === ' ': key (unlike code) is 'Enter' for NumpadEnter too, and Space is handled with preventDefault() so it activates the button instead of scrolling the page.

The issue also suggested replacing the pattern with a real <button> clicking the hidden input via a ref. That variant needs ref.current?.click() whose null branch is unreachable in tests, which would break the 100% coverage gate for no behavioral gain, so the minimal handler fix won.

Tests

The existing keyboard test now covers all four cases: an unrelated key does nothing, Enter, NumpadEnter, and Space all trigger the click, and Space's default is prevented. It fails on main without the fix (verified via git stash).

Coverage stays at 100%.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (df741b3) to head (a73244c).

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #40   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            9         9           
  Lines          209       210    +1     
  Branches        55        55           
=========================================
+ Hits           209       210    +1     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.