feat: floating feedback button on all pages

[guidefari]

Context

Discussed need for a low-friction way to collect user feedback across the app.

Description

Add a fixed-position floating feedback button that appears on all pages via AppShell. Clicking opens a modal with a simple form.

Acceptance Criteria

• Floating button fixed to screen (bottom-right corner typical)
• Opens modal on click — no page navigation
• Form: textarea (required) + email (optional)
• Auto-captures current page URL on submit
• Integrated into AppShell so it renders everywhere
• Backend: submit via Resend email or webhook (Notion/Google Sheet) — TBD

Technical Notes

• Mount in apps/www/src/components/Layout/AppShell.tsx
• Use window.location.href to capture page context at submission time
• Keep modal as a small self-contained component

Related

• apps/www/src/components/Layout/AppShell.tsx
• apps/www/src/components/Layout/Footer.tsx

[linear]

OPS-99