feat: build the desktop MVP shell mockup

[ibourgeois]

Summary

• replace the old diagnostic-first desktop page with a branded MVP shell built from reusable Blade components
• turn the sidebar, center conversation area, and context rail into interactive local demos with search, workspace/chat flows, and session-backed messaging
• add Blade MDI icons, theme switching, logo variants, and supporting tests for the staged shell experience

Testing

• vendor/bin/pint --dirty --format agent
• php artisan test --compact tests/Feature/DesktopShellTest.php tests/Feature/DesktopUiFeatureFlagTest.php
• git diff --check

[Copilot]

Pull request overview

This PR replaces the previous diagnostic-first desktop landing page with a branded “MVP workspace shell” experience, gated by Pennant feature flags, and backed by reusable Blade components, theme styling, icons, and feature tests.

Changes:

• Rebuild / as the desktop MVP shell mock (sidebar + conversation area + context rail), including interactive demo behaviors and session-backed messaging.
• Introduce new desktop Blade components (navigation, panels, profile menu, modals, pills) and Nord-themed shell styles/logo variants.
• Add/adjust feature and shell tests, and pull in Blade MDI icon support via Composer.

Reviewed changes

Copilot reviewed 20 out of 23 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
app/Http/Controllers/HomeController.php	Builds mock workspace state, resolves Pennant/desktop flags, selects active workspace, and passes view data for the new shell.
resources/views/welcome.blade.php	Replaces the old welcome/diagnostics page with the new shell layout + interactive demo logic.
resources/views/components/desktop/status-pill.blade.php	New pill component for compact status labels in the shell.
resources/views/components/desktop/profile-menu.blade.php	New profile dropdown with theme switching controls.
resources/views/components/desktop/panel.blade.php	New panel wrapper component for shell sections/empty states.
resources/views/components/desktop/nav-section.blade.php	New navigation section component (optionally collapsible).
resources/views/components/desktop/nav-item.blade.php	New navigation row item component used across workspace/room/chat lists.
resources/views/components/desktop/modal.blade.php	New <dialog> wrapper for shell modal demos.
resources/views/components/desktop/message-bubble.blade.php	New message UI component (used as a building block for conversation UI).
resources/views/components/desktop/list-card.blade.php	New list card component for compact summary rows.
resources/views/components/desktop/icon-button.blade.php	New icon button component (used as “create” affordances).
resources/views/components/desktop/feature-card.blade.php	Restyles existing card component to match the new shell theme.
resources/views/components/desktop/window-frame.blade.php	Restyles the frame component to match the new Nord palette shell.
resources/views/components/desktop/workspace-status-card.blade.php	Removes old diagnostic-era workspace status card.
resources/views/components/desktop/runtime-status-card.blade.php	Removes old diagnostic-era runtime status card.
resources/views/components/desktop/sidebar-block.blade.php	Removes old diagnostic-era sidebar block component.
resources/css/app.css	Adds shell theme variables/utilities and theme switching styles.
public/katra-logo.svg	Adds dark-mode logo asset.
public/katra-logo-light.svg	Adds light-mode logo asset.
tests/Feature/DesktopShellTest.php	Updates shell assertions and adds workspace switching coverage.
tests/Feature/DesktopUiFeatureFlagTest.php	Updates assertions and adds coverage for hiding the shell via the MVP flag.
composer.json	Adds postare/blade-mdi dependency for <x-mdi-*> icon components.
composer.lock	Locks new icon dependencies (blade-icons, blade-mdi).

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