Fix test failures on Ubuntu and other platforms (issue #486)

Fixes test suite to run cleanly across different platforms (macOS, Linux, Windows)
after the Rails 5→8 upgrade and UI/UX overhaul.

## Issues Fixed

1. **Firefox/Selenium driver errors**: Removed deprecated Poltergeist/PhantomJS
   configuration and properly configured Selenium with headless Chrome. This
   works across all platforms without requiring Firefox.

2. **CSS selector errors** ('Unable to find css ".signup"'): The UI/UX overhaul
   removed the .signup CSS class. Updated the login helper to work with the
   new login form structure.

3. **Ambiguous Login button**: The new UI has both a Login button and Login link.
   Changed from `click_on "Login"` to `click_button "Login"` to be specific.

4. **Deprecation warning**: Opted into Rails 8.1 behavior for to_time timezone
   preservation to eliminate deprecation warnings.

## Changes

- spec/support/capybara_shared.rb:
  * Removed deprecated Poltergeist/PhantomJS configuration
  * Configured Selenium with headless Chrome
  * Updated login helper to work with new UI (removed .signup/.actions selectors)
  * Changed click_on to click_button for specificity

- spec/spec_helper.rb:
  * Removed conflicting Capybara.javascript_driver override that was forcing
    selenium_headless (which tried to use Firefox)

- config/application.rb:
  * Added config.active_support.to_time_preserves_timezone = :zone to opt into
    Rails 8.1 behavior and eliminate deprecation warning

## Test Results

Before: 43 failures (driver errors, CSS selector errors)
After: 46 examples, 0 failures, 14 pending ✅

The 14 pending specs are expected - they verify vulnerabilities still exist.

## Platform Requirements

JavaScript tests now require Chrome/Chromium to be installed:
- macOS: Chrome is usually installed
- Ubuntu: `sudo apt-get install chromium-browser chromium-chromedriver`
- Windows: Chrome is usually installed

Fixes #486

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

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

spec/support/capybara_shared.rb

@@ -37,64 +37,22 @@ end
 
 def login(user)
   visit "/"
-  within(".signup") do
-    fill_in "email", with: user.email
-    fill_in "password", with: user.clear_password
-  end
-  within(".actions") do
-    click_on "Login"
-  end
+  fill_in "email", with: user.email
+  fill_in "password", with: user.clear_password
+  click_button "Login"
 end
 
-##Hack to fix PhantomJS errors on Mavericks - https://gist.github.com/ericboehs/7125105
-module Capybara::Poltergeist
-  class Client
-    private
-    def redirect_stdout
-      prev = STDOUT.dup
-      prev.autoclose = false
-      $stdout = @write_io
-      STDOUT.reopen(@write_io)
+# Configure Selenium with headless Chrome for JavaScript testing
+# This works across macOS, Linux, and Windows without requiring Firefox
+Capybara.register_driver :selenium_chrome_headless do |app|
+  options = Selenium::WebDriver::Chrome::Options.new
+  options.add_argument("--headless")
+  options.add_argument("--disable-gpu")
+  options.add_argument("--no-sandbox")
+  options.add_argument("--disable-dev-shm-usage")
+  options.add_argument("--window-size=1920,1080")
 
-      prev = STDERR.dup
-      prev.autoclose = false
-      $stderr = @write_io
-      STDERR.reopen(@write_io)
-      yield
-    ensure
-      STDOUT.reopen(prev)
-      $stdout = STDOUT
-      STDERR.reopen(prev)
-      $stderr = STDERR
-    end
-  end
+  Capybara::Selenium::Driver.new(app, browser: :chrome, options: options)
 end
 
-class WarningSuppressor
-  IGNORE_PATTERNS = [
-    /QFont::setPixelSize: Pixel size <= 0/,
-    /CoreText performance note:/,
-    /WARNING: Method userSpaceScaleFactor/
-  ]
-
-  def write(message)
-    if ignore?(message)
-      0
-    else
-      puts(message)
-      1
-    end
-  end
-
-  private
-
-  def ignore?(message)
-    IGNORE_PATTERNS.any? { |regexp| message =~ regexp }
-  end
-end
-
-Capybara.register_driver :poltergeist do |app|
-  Capybara::Poltergeist::Driver.new(app, phantomjs_logger: WarningSuppressor.new, timeout: 60)
-end
-
-Capybara.javascript_driver = :poltergeist
+Capybara.javascript_driver = :selenium_chrome_headless