Add desktop settings shell and doctor panel

[wesbillman]

Summary

• replace the inline desktop settings view with a dedicated settings shell that has its own section sidebar and close control
• make Cmd+, / Ctrl+, toggle settings open and closed
• add a Doctor settings panel for local Sprout binaries, ACP runtime discovery, and troubleshooting inputs
• move local binary setup guidance out of agent creation and into Settings > Doctor
• update desktop E2E coverage for the new settings navigation and doctor panel

Testing

• source ./bin/activate-hermit && cd desktop && pnpm check
• source ./bin/activate-hermit && cd desktop && pnpm build
• source ./bin/activate-hermit && cd desktop && pnpm exec playwright test tests/e2e/profile.spec.ts --project=integration
• git push -u origin desktop-settings-shell (pre-push hook ran desktop checks/build, Tauri cargo check, workspace cargo clippy, and ./scripts/run-tests.sh unit)