feat(desktop): add request workbench shell

[kev1n77]

Summary

• add a React 19 + TypeScript request workbench with search, provider/app/tool/error filters, keyboard navigation, resizable panes, and Anatomy/Timeline/Raw inspectors
• add the Tauri 2 desktop shell with tray lifecycle, close-to-tray behavior, constrained capabilities, bundled icons, and a synthetic credential-free workspace fixture
• add frontend and Windows/macOS native CI checks, local development commands, and progress tracking updates

Verification

• npm run desktop:check
• npm run desktop:build
• cargo fmt --manifest-path apps/desktop/src-tauri/Cargo.toml -- --check
• cargo test --manifest-path apps/desktop/src-tauri/Cargo.toml
• cargo check --manifest-path apps/desktop/src-tauri/Cargo.toml
• cargo fmt --all -- --check
• cargo test --workspace --all-targets
• cargo clippy --workspace --all-targets -- -D warnings
• local Vite HTTP smoke check returned 200

Notes

• workspace data is synthetic and contains no real prompts or credentials
• live capture and encrypted persistence are intentionally deferred to follow-up increments