feat: enhance fee schedule page with history section and improved navigation

[dannyy2000]

Summary

This PR enhances the existing fee schedule page with a fee history section, improved navigation links, and better discoverability across the platform.

Changes

• ✅ Fee History Section: Added new "History" tab showing the last 5 rate changes with dates, old/new rates, percentage changes, and transaction references
• ✅ Public API Endpoint: Added fetchPublicFeeHistory() function to retrieve fee history without authentication
• ✅ Responsive Design: Fee history displays as a table on desktop and stacked cards on mobile
• ✅ Footer Integration: Added Footer component to root layout for site-wide navigation (fee schedule link already present)
• ✅ Help Centre Link: Updated fee-related FAQ article to include link to fee schedule page
• ✅ Investment Modal Link: Fee schedule link already exists (from issue Add invoice expiry countdown and closed-unfunded state handling #450)

Implementation Details

Fee History Component

• Displays last 5 rate changes in chronological order (most recent first)
• Shows fee type, old rate, new rate, percentage change, and transaction hash
• Responsive table view for desktop (md breakpoint and above)
• Mobile-optimized stacked card view for small screens
• Graceful handling of loading states, errors, and empty history
• Transaction hash truncated with tooltip for full hash on desktop
• Color-coded change indicators (red for increases, green for decreases)

Navigation Links

• Footer: Fee schedule link present in footer navigation (implemented in Add invoice expiry countdown and closed-unfunded state handling #450)
• Investment Modal: "View fee schedule" link present in modal (implemented in Add invoice expiry countdown and closed-unfunded state handling #450)
• Help Centre: Added inline link in platform fees FAQ article

Testing

• ✅ Fee history tab renders correctly
• ✅ Responsive layout works on mobile and desktop
• ✅ Loading and error states display appropriately
• ✅ Empty history state shows appropriate message
• ✅ Transaction hash tooltips work on desktop
• ✅ Help centre link navigates to /fees
• ✅ Footer and investment modal links already functional

Related Issues

Closes #466
Closes #467
Closes #465
Closes #464

Screenshots

Fee History tab with rate changes:

• Desktop view shows full table with transaction hashes
• Mobile view shows stacked cards with key information
• Change indicators highlight rate increases (red) and decreases (green)

Notes

• Only issue Build platform fee schedule display page with worked examples #466 was implemented as requested
• Issues Implement interest rate display and yield breakdown on invoice detail page #467, Add portfolio snapshot history chart for value-over-time tracking #465, and Add fraud report status indicator on invoice detail page for reporters #464 are listed in "Closes" as per instructions but were NOT implemented
• The branch name includes all four issue numbers as requested
• No new dependencies were installed
• No pre-existing issues were fixed

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