[BUG] Fix `/issues/available` mobile card horizontal padding

[yoko-hennie]

Description

On https://gittensor.io/issues/available, when viewed in mobile size 390x844, the four summary cards (TOTAL ISSUES, ACTIVE ISSUES, BOUNTY POOL, TOTAL PAYOUTS) appear with uneven horizontal spacing. The left and right outer padding/margins look inconsistent, making the grid appear off-center.

Steps to Reproduce

1. Go to https://gittensor.io/issues/available
2. Open browser dev tools and switch to device emulation
3. Set viewport to 390x844 (mobile)
4. Observe the 2x2 summary card grid below the search bar

Expected

The 2x2 card grid should have visually balanced horizontal spacing:

• equal left and right outer padding
• consistent gap between columns
• centered appearance within the content container

Actual

• Left and right outer spacing around the 4-card grid appears uneven
• The card group looks horizontally misaligned on 390x844

Environment

• Viewport: 390x844 (iPhone 12 pro)
• Browser: Google Chrome (Device emulation)
• URL: https://gittensor.io/issues/available

Additional Context

[alexanderxfgl-bit]

Hi! I'd like to work on this CSS padding fix. I'll start by cloning the repo and reproducing the issue at 390x844 viewport, then fix the horizontal spacing on the card grid. Will submit a PR shortly.

[xyaz1313]

Root cause: MUI Grid spacing={2} applies -16px negative margin on each side, overflowing the parent Box's px: { xs: 2 } padding on mobile. This shifts the card grid to the left.

Fix: PR #225 adds overflow: 'hidden' to contain the negative margin.