Add About page with feedback form

[dhruv-gajwa]

Summary

• Adds /app/about route with an About page accessible from the sidebar nav
• Page shows app info (version, purpose, tech-stack badges)
• Includes a small feedback form (category select, subject, message) using React Hook Form + Zod validation
• On submit fires a pendo.track('feedback_submitted', {...}) event and shows a Mantine success notification
• All interactive elements carry data-pendo-id attributes via the typed PENDO_IDS.about.* namespace

Test plan

• Navigate to /app/about via the "About" nav link (info icon, bottom of sidebar)
• Verify About section renders with version, purpose card, and tech-stack badges
• Submit form with empty fields — confirm Zod validation errors appear
• Submit form with valid inputs — confirm success toast appears and form resets
• Confirm pendo.track('feedback_submitted', ...) fires in browser console

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