feat: design system polish (in-page headers, indies tabs, sidebar collapse removal)

[paulocastellano]

Summary

Branch design-system polish across the app: in-page page headers replacing the global AppHeader slots on Calendar / Edit / Show, redesigned shadcn Tabs to match the indies button vocabulary, removed the desktop sidebar collapse, and a few targeted UX fixes.

• In-page page headers: Calendar, Edit (post), and Show (post) now render their controls in their own ink-bordered bar inside the layout instead of pushing them through #header / #header-actions slots. Calendar header uses a 3-col grid with the date title centered. Show header swapped for back-button-left + date/status-right.
• Sidebar collapse removed: dropped Cmd+B keyboard shortcut, forced defaultOpen=true (ignore persisted cookie), toggleSidebar is now a no-op on desktop. Mobile sheet behavior preserved. AppSidebar now uses collapsible="offcanvas" with the icon-mode logic in Create Post button cleaned up.
• Tabs redesign (global): each TabsTrigger is now a standalone button-style sticker (border-2 border-foreground rounded-md shadow-xs), matching the rest of the system. Active state uses bg-amber-200 mirroring the "POST" badge from post-templates. TabsList is just a flex row with gap-2 (no outer container).
• Global control sizing: bumped Button (default h-9→h-10, sm h-8→h-9, lg h-10→h-11, icons +1), Input (h-9→h-10), SelectTrigger (default h-9→h-10, sm h-8→h-9), and HexColorInput swatch (size-9→size-10). Tabs match new h-10.
• Analytics: replaced the second-column accounts sidebar with a Popover + Command AnalyticsAccountSelector in the header (avatar + handle, searchable by name/username/platform). Localized all metric labels backend-side via analytics.metrics.* keys + multi-locale keyword matching for the icon mapping. Removed lang/{en,pt,es}/analytics.php channels key.
• Show page: capped post preview Card to max-w-xl, preserve natural aspect ratio for single-image posts (object-contain, max-h-[480px]); dropped redundant Platforms/Published/Failed stats grid; metric loading bug fixed (hoisted useHttp out of onMounted, response array read at root).
• Assets: search inputs in GalleryBrowser (Uploads / Unsplash / Giphy) bumped to h-12 for comfortable browsing.
• Workspace creation flow: WorkspaceController@store now always redirects to /accounts?openDialog=true (dropped the $isFirstWorkspace branch). SocialController@index reads ?openDialog=true and ships openDialog: bool as an Inertia prop, so accounts/Index.vue opens AddSocialDialog automatically without touching URLSearchParams. Renamed the i18n key workspaces.create.first_workspace_success → reused success with the social-account copy.
• Auth/legal copy: moved the legal text out of AuthSplitLayout into Register.vue directly (only consumer), with selfHosted check via usePage(). Dropped the showLegal prop from AuthLayout + AuthSplitLayout.

Test plan

• Navigate /calendar, /posts/{id}/edit, /posts/{id} — confirm header bar renders inside the page (no global app header), full-width canvas, controls aligned
• On desktop, confirm Cmd+B does nothing and the sidebar can't be collapsed; mobile drawer still opens via the floating trigger
• Confirm Tabs render as standalone sticker buttons in Settings tabs, Calendar Day/Week/Month, post editor sidebar tabs
• /analytics: pick an account from the popover, verify search by display name / username / platform; metrics labels render in pt-BR with correct sticker icons
• /posts/{id} with multi-platform published post: per-platform metrics fetch resolves (no infinite spinner)
• Create first workspace → lands on /accounts?openDialog=true with the connect dialog auto-open
• Create non-first workspace → same destination/behavior
• /register (saas mode) shows legal block; setting TRYPOST_SELF_HOSTED=true hides it