## ADDED Requirements

### Requirement: Alt+LMB orbit navigation

The viewport SHALL orbit the camera around the focal point when the user holds Alt and drags with the left mouse button.

#### Scenario: Alt+LMB drag orbits the camera
- **WHEN** the user holds Alt and drags with the left mouse button inside the viewport
- **THEN** the camera orbits around the focal point based on the drag delta

#### Scenario: LMB without Alt does not orbit
- **WHEN** the user drags with the left mouse button without holding Alt
- **THEN** no orbit occurs and the click is forwarded for prim selection

### Requirement: Alt+MMB pan navigation

The viewport SHALL pan the camera when the user holds Alt and drags with the middle mouse button.

#### Scenario: Alt+MMB drag pans the camera
- **WHEN** the user holds Alt and drags with the middle mouse button inside the viewport
- **THEN** the camera pans horizontally and vertically based on the drag delta

### Requirement: Alt+RMB dolly navigation

The viewport SHALL dolly (zoom) the camera when the user holds Alt and drags with the right mouse button. Vertical drag upward moves the camera closer; downward moves it farther.

#### Scenario: Alt+RMB drag dollies the camera
- **WHEN** the user holds Alt and drags vertically with the right mouse button inside the viewport
- **THEN** the camera dollies in or out based on the vertical drag delta

### Requirement: Scroll zoom without Alt

The viewport SHALL zoom the camera when the user scrolls the mouse wheel, without requiring the Alt modifier.

#### Scenario: Scroll wheel zooms
- **WHEN** the user scrolls the mouse wheel while hovering over the viewport
- **THEN** the camera zooms in or out based on the scroll direction

### Requirement: Legacy input mappings removed

The previous input mappings (LMB for orbit, MMB for pan, Shift+LMB for pan) SHALL be replaced entirely by the Maya-style Alt+button scheme.

#### Scenario: MMB without Alt does not pan
- **WHEN** the user drags with the middle mouse button without holding Alt
- **THEN** no pan occurs

#### Scenario: Shift+LMB does not pan
- **WHEN** the user holds Shift and drags with the left mouse button
- **THEN** no pan occurs
