fix: security headers, DOMPurify sanitization, and localStorage audit

[teeschima]

Closes #27

Summary

Implements comprehensive security hardening for the StepFi-Web application across 5 areas.

Changes

1. Security Headers (vercel.json, netlify.toml)

• Content-Security-Policy: Restrictive policy allowing only self sources, with explicit allowlists for styles (unsafe-inline for Tailwind/Framer Motion), images (data:), API connections (stepfi-api.onrender.com), and fonts. Sets frame-ancestors 'none' and base-uri 'self'.
• X-Frame-Options: DENY
• X-Content-Type-Options: nosniff
• Referrer-Policy: strict-origin-when-cross-origin
• Permissions-Policy: camera, microphone, geolocation all disabled
• Strict-Transport-Security: max-age=31536000; includeSubDomains; preload

2. DOMPurify Sanitization (src/lib/sanitize.ts)

• Created utility with sanitizeText() (strips all HTML) and sanitizeHtml() (safe HTML)
• Applied to all 5 user-generated content fields:
  • vouch.message in LearnerProfile
  • product.name, product.description in VendorDashboard
  • key.label in VendorDashboard
  • loan.product in VendorDashboard

3. HTTPS Enforcement

• HSTS header added to both deployment configs
• Platform-level HTTPS enforcement on Vercel and Netlify

4. localStorage Audit

• api.ts: Replaced direct localStorage.getItem('accessToken') with reader that parses the zustand-persisted store (stepfi-user), eliminating duplicate storage keys
• user.store.ts: Removed redundant localStorage.setItem/removeItem calls (zustand persist middleware already handles persistence)
• Standardized on single storage key via zustand persist

5. Subresource Integrity

• No external CDN assets exist — all scripts bundled via Vite, so SRI is not applicable

Verification

• npm run build passes (tsc + vite build)

[EmeditWeb]

@teeschima fix CI issues

The Navbar.tsx fix is already in another open PR.

Before working on your branch, pull the latest main:

git checkout main
git pull origin main
git checkout your-branch-name
git rebase main

Then run:
npm run lint 2>&1 | tail -5

If the error is gone, push:
git push origin your-branch-name --force-with-lease

If the error still shows after rebasing, apply this fix
manually in src/components/layout/Navbar.tsx:

Remove this useEffect:
useEffect(() => {
setMobileOpen(false)
}, [pathname])

Replace with onClick on each mobile nav Link:

setMobileOpen(false)} ... >

Then:
npm run lint 2>&1 | tail -5
npm run build 2>&1 | tail -5

Both must exit 0 before pushing.

[EmeditWeb]

fix CI issues

[EmeditWeb]

Closing this PR. See the reset notice on the other closed PRs: re-read CONTRIBUTING.md and the PR template, follow the context/ files, and pass all CI checks before resubmitting.