Enhance blog hero section with subtle background styles / theme effects

[ig-imanish]

Context

The current blog hero is clean but visually flat - solid dark background with centered text. It works, but feels too basic for a page aimed at people who ship open source.

Problem

Hero section lacks any visual depth or atmosphere. No gradients, noise, grid, glow, or subtle motion. Feels static compared to the rest of the product.

Proposed Direction

Add lightweight background treatment that still keeps the "no fluff" tone:

• Soft radial / linear gradient (very low opacity)
• Subtle noise texture or grain overlay
• Optional faint grid / dot pattern
• Very mild glow behind the headline (CSS only)
• Keep it performance-friendly (no heavy canvas / Three.js)

Ideally support a couple of theme variants or at least look intentional in both light/dark if we ever expand.

Acceptance Criteria

• Hero background has visible but restrained visual interest
• Does not hurt LCP / CLS
• Works on mobile (no excessive animation)
• Matches overall Ossium aesthetic (dark, minimal, sharp)

Notes

Reference the current screenshot.

Priority is low - polish, not core feature.