Fix remaining CSS selector and form field issues from UI/UX overhaul

This addresses the remaining test failures @jasnow reported in issue #486.

Fixes:
1. Ambiguous Login button - Changed from click_button "Login" to
   find("input[type='submit'][value='Login']").click to specifically
   target the form submit button and avoid the header Login button

2. Fixed password_complexity_spec field names:
   - user_email → email
   - user_first_name → first_name
   - user_last_name → last_name
   - user_password → password
   - user_password_confirmation → password_confirmation
   - Submit → Create Account (correct button text)

3. Applied same selector fix to login helper in capybara_shared.rb

These changes complete the test suite fixes for the new UI that was
introduced in the file upload UX improvements.

Related: #486

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

spec/support/capybara_shared.rb

@@ -39,7 +39,7 @@ def login(user)
   visit "/"
   fill_in "email", with: user.email
   fill_in "password", with: user.clear_password
-  click_button "Login"
+  find("input[type='submit'][value='Login']").click
 end
 
 # Configure Selenium with headless Chrome for JavaScript testing