fix(security): update postcss and glib dependencies to resolve Depend…

[vkshdev]

Summary:
This Pull Request resolves open Dependabot security vulnerabilities (PostCSS and glib) in a single grouped update, enforces safe package overrides across the workspace, and cleans up desktop CSS syntax.

Key Changes:

1. Security Dependency Upgrades

• PostCSS (High Severity): Enforced postcss >= 8.5.18 via package.json overrides and updated postcss from 8.5.15 to 8.5.23 in pnpm-lock.yaml.
• glib (Moderate Severity): Updated Rust glib and related workspace dependencies in Cargo.lock.

2. CSS Syntax Cleanup

• apps/desktop/src/styles/globals.css: Removed duplicate .app-shell rule blocks to ensure clean stylesheet compilation for the desktop app.