[Feature Request]: Keyboard shortcuts to switch between open PDFs

[enjoyandlove]

Feature Description

Add keyboard shortcuts to switch between currently open PDF files/tabs without using the mouse.

Current behavior allows multiple PDFs to be open, but users must click to change the active document. This slows down keyboard-first workflows and accessibility use cases.

Proposed behavior:

• Provide forward/backward tab cycling across open PDFs.
• Use browser-safe defaults in web builds (avoid Ctrl+Tab because browsers reserve it for browser tabs).
• Optionally allow Ctrl+Tab / Ctrl+Shift+Tab in desktop (Tauri) builds where feasible.
• Show a visible active-tab indicator when navigation occurs via keyboard.
• Handle edge cases cleanly (0 or 1 open PDF, closed tab during navigation, wrapping at ends).

Accessibility expectations:

• Keep focus stable (do not steal focus from text controls unexpectedly).
• Announce active document change via an aria-live region (e.g., "Switched to , tab 2 of 5").
• Ensure active tab uses proper role="tab" / aria-selected="true" semantics.
• Preserve visible focus indicators for keyboard users.

Motivation

This improves keyboard-only navigation and reduces reliance on mouse interaction, especially for users reviewing many PDFs in sequence.

It aligns with accessibility and productivity goals:

• Faster document comparison/review workflows.
• Better support for assistive tech and power users.
• More consistent desktop-app behavior where tab switching via keyboard is expected.

Additional Information

UX behavior recommendations:

• Always cycle (wrap from last -> first, first -> last).
• Briefly highlight the selected PDF tab after keyboard switch.
• Optional toast/help hint the first few times user uses the shortcut.
• If only one file is open, do nothing (or optional subtle status message).
• If no file is open, shortcuts are ignored.

Cross-platform notes:

• Browser environments may not reliably expose reserved combos (Ctrl+Tab), so defaults must avoid them.
• Desktop runtime can safely support Ctrl+Tab, but should still provide remapping for OS/layout differences.
• macOS considerations for future customization: allow Cmd+Option+Arrow style alternatives where appropriate.

No duplicate confirmation:

• I have verified that there are no existing feature requests similar to this request.