## Context

The app currently uses a minimal MudLayout with just MudAppBar (Dense) + MudMainContent, and a single page at `/`. To support multiple pages, we need standard MudBlazor navigation: a collapsible MudDrawer with a NavMenu component.

## Goals / Non-Goals

**Goals:**
- Add collapsible MudDrawer with hamburger toggle in the AppBar
- Create a NavMenu component with a "Sales Assistant" link
- Move chat page to `/sales-assistant` route
- Maintain the Blazor tutorial style with inline comments

**Non-Goals:**
- Adding multiple pages beyond the existing chat (just the navigation structure)
- Changing the AppBar from Dense to regular
- Adding a default landing page (redirect `/` → `/sales-assistant` instead)

## Decisions

### MudDrawer configuration
- **Variant**: `DrawerVariant.Mini` — collapses to icon-width rather than fully hiding, so the user always sees the nav rail
- **Alternative considered**: `DrawerVariant.Responsive` — auto-hides on small screens. Rejected because Mini gives a more consistent desktop experience and the app is desktop-first.
- **ClipMode**: `DrawerClipMode.Always` — drawer sits below the AppBar, not beside it

### NavMenu as separate component
- Extract `NavMenu.razor` into `Layout/` alongside MainLayout rather than inlining nav links
- This is standard Blazor project structure and keeps MainLayout focused on shell layout
- The NavMenu will use `MudNavMenu` with `MudNavLink` items

### Route change: `/` → `/sales-assistant`
- The chat page moves to `/sales-assistant` to match navigation naming
- Add a redirect component at `/` that navigates to `/sales-assistant` on init
- This avoids a blank landing page while keeping the URL structure clean

### AppBar hamburger toggle
- Add `MudIconButton` with `Icons.Material.Filled.Menu` as the first element in the AppBar
- Toggle `_drawerOpen` bool that binds to `MudDrawer.Open`

## Risks / Trade-offs

- **Chat container height**: Currently uses `calc(100vh - 48px)` assuming Dense AppBar (48px). MudDrawer with ClipMode.Always doesn't affect vertical calc, so this should remain correct. Verify after implementation.
- **Breaking bookmarks**: Anyone bookmarking `/` will need to update to `/sales-assistant`. Mitigated by the redirect at `/`.