fix(landing): design audit fixes — hamburger menu, dead links, branding, spacing (#117)

* fix(landing): design audit fixes — hamburger menu, dead links, branding, spacing

- Add mobile hamburger menu with animated open/close and click-outside dismiss
- Create Privacy and Terms pages (footer links were dead # anchors)
- Change "Decision Tree Platform" to "AI-Powered Troubleshooting for MSPs" on login, register, and HTML title
- Fix register page icon color (was red/coral via CSS invert, now uses BrandLogo directly)
- Replace "0 Ticket Notes Written by Hand" stat with "100% Auto-Generated Documentation"
- Increase nav link touch targets to 44px minimum
- Fix heading hierarchy: section titles are now <h2>, standardize H3 to 1.25rem
- Tighten section spacing (6rem → 4rem padding, remove extra 5rem spacer)
- Add color-scheme: dark to HTML element
- Replace all transition: all with specific properties (10 occurrences)
- Fix loading ellipsis (... → …)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix(mobile): responsive modals + landing preview overflow

- PrepareSessionModal: bottom-sheet on mobile, centered on desktop
- IntakeFormModal: bottom-sheet on mobile, responsive padding
- ShareTreeModal: bottom-sheet on mobile, full-width on small screens
- Landing preview: hide URL bar and window controls on mobile (<900px)
  to prevent 189px horizontal overflow

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix(mobile): collapse search bar to icon on mobile

On mobile (<640px), the full search bar with placeholder text and ⌘K
badge was taking too much space in the topbar. Now shows just a
magnifying glass icon that opens the same command palette on tap.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: chihlasm <michael@resolutionflow.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/library/ShareTreeModal.tsx

@@ -112,7 +112,7 @@ export function ShareTreeModal({ tree, isOpen, onClose }: ShareTreeModalProps) {
   if (!isOpen) return null
 
   return (
-    <div className="fixed inset-0 z-50 flex items-center justify-center">
+    <div className="fixed inset-0 z-50 flex items-end justify-center p-0 sm:items-center sm:p-4">
       {/* Backdrop */}
       <div
         className="absolute inset-0 bg-black/80 backdrop-blur-xs"
@@ -120,7 +120,7 @@ export function ShareTreeModal({ tree, isOpen, onClose }: ShareTreeModalProps) {
       />
 
       {/* Modal */}
-      <div className="relative w-full max-w-lg bg-card border border-border rounded-2xl shadow-lg">
+      <div className="relative w-full max-w-full rounded-t-2xl bg-card border border-border shadow-lg sm:max-w-lg sm:rounded-2xl">
         {/* Header */}
         <div className="flex items-center justify-between border-b border-border px-6 py-4">
           <h2 className="text-lg font-semibold text-foreground">Share Tree</h2>