Add Tusk to App Stories

[huacnlee]

Summary

• Add Tusk to App Stories as a developer tool for macOS, Windows and Linux.
• Include a concise product introduction covering connection management, data editing, SQL queries and user-controlled AI query drafting.
• Archive the upstream full-window PNG unchanged and retain its attribution and MIT license.

Source verification

Verified against the official Tusk repository at 5285238fb7501cce482b4b67d2e8f7d279e675fd:

• Cargo.toml declares gpui-kit 0.6.
• README documents supported platforms and the included features.
• Original screenshot is preserved at its original 1920 × 1149 resolution, with the full window, title controls, edges and corners visible. No resizing or cropping.

Validation

• bun install --frozen-lockfile (Bun 1.4.0)
• bun test: 22 passed, 0 failed
• bun run validate: 64 app manifests and screenshots validated
• git diff --cached --check
• PNG decoded successfully; its Git blob hash and the license hash match upstream exactly