Add weekly riding input, inline feedback, and weekly-based savings calculations

[moustyb]

Motivation

• Provide a more realistic usage model by letting users specify how many days per week they bike so savings scale with actual riding frequency.
• Improve UX by replacing blocking alert()s with an inline, accessible status message to communicate validation and success.
• Make monthly/yearly projections more consistent by deriving them from weekly totals and present results with clearer number formatting.

Description

• Added a Days biked per week numeric input and an accessible inline message element (#formMessage) to index.html.
• Reworked script.js to add constants for DAYS_PER_WEEK, WEEKS_PER_YEAR, and MONTHS_PER_YEAR, to validate the new input, and to replace alert-based validation with setMessage() which updates the inline status element.
• Changed calculations to compute CO₂, gas, and money saved on a weekly basis and derive monthly/yearly projections from weekly totals, adjusted the medal logic to compare annual biking distance using the chosen weekly schedule, and added formatNumber() for locale-friendly output.
• Added .form-message success/error styles to style.css for the inline status feedback.

Testing

• Ran a static JavaScript syntax check with node --check script.js, which completed successfully.
• Served the app with python3 -m http.server 4173 and ran an automated Playwright script that fills the form, submits a sample calculation, and captured a screenshot to verify UI and result rendering, which succeeded.
• Manual visual verification was captured via the generated screenshot from the headless run.

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Codex Task

[cloudflare-workers-and-pages]

Deploying co2-calculator with    Cloudflare Pages

Latest commit:	1b861d5
Status:	✅  Deploy successful!
Preview URL:	https://40bee685.co2-calculator-atb.pages.dev
Branch Preview URL:	https://codex-upgrade-the-code.co2-calculator-atb.pages.dev

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Project	Deployment	Actions	Updated (UTC)
co-2-calculator	Ready	Preview, Comment	Feb 14, 2026 11:16pm