Feat: redesign responsive navigation for mobile and narrow screens

[wolfyres]

Closes #71

Context

A desktop three-pane layout cannot simply collapse on smaller screens. This PR implements a dedicated mobile navigation model—transitioning fluidly between a folder drawer, message list, and reader view—ensuring a coherent and native-feeling experience on mobile devices.

🛠️ Key Changes

Navigation Routing: Implemented distinct mobile routes for the folder drawer, message list, and reader views.

Compose Sheet: Added a responsive bottom sheet for the compose view with robust state management.

State Preservation: Engineered safe back-navigation behavior to guarantee draft states are never lost when users swipe or tap back.

UI Refinements: Adjusted responsive density for smaller screens and integrated proof details natively into the mobile reader flow.

✅ Acceptance Criteria Verified

[x] Core workflows (read, reply, allow, block) function flawlessly at a 320px viewport width.

[x] Eliminated all horizontal overflow across mobile routes.

[x] Back navigation accurately preserves draft state in all scenarios.

[x] Touch targets meet standard accessibility guidance (minimum 44x44px padding).

🧪 QA & Success Signal

Ready for UX validation and usability testing. Our target success signal is that mobile task completion times for core workflows remain within 20% of the desktop baseline.

[kryputh]

@wolfyres add proper pr description

[wolfyres]

@wolfyres add proper pr description

Doneeeeeeeee