refactor: adopt shared Input/Textarea components (#101)

* refactor: adopt shared Input/Textarea components across 15 files

Replace 42 raw <input>/<textarea> elements with <Input>/<Textarea>
from components/ui/. Consistent focus states, error handling, and
styling across all form fields.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* refactor: replace hardcoded rgba/hex colors with Tailwind tokens

- rgba(255,255,255,0.xx) → bg-white/[0.xx], border-white/[0.xx]
- rgba(6,182,212,0.3) → border-primary/30 (focus states)
- #0a0a0a → bg-background
- Inline style hex colors → var(--color-primary), var(--color-brand-gradient-to)
- 28 files updated, zero hardcoded rgba() patterns remaining

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: add PageMeta to 16 pages for SEO and proper browser tab titles

Public pages (Login, Register, Forgot/Reset Password, Verify Email,
Survey Thank You) get descriptions for SEO. Authenticated pages
(Dashboard, Flow Library, My Flows, Session History, AI Assistant,
Account Settings, Step Library, My Shares, Feedback, Guides) get
proper tab titles.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: add page transitions and staggered list animations

- ViewTransitionOutlet: wraps Outlet with fade-in-up animation keyed
  to route path. Sidebar/topbar stay still, only content area animates.
- StaggerList: reusable component that cascades children with
  incremental delay (50ms default). Pure CSS via @utility stagger-item.
- Applied stagger to TreeGridView, MyTreesPage cards, SessionHistoryPage.
- New stagger-fade-in keyframe in @theme block.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: ViewTransitionOutlet needs h-full for React Flow canvas

The wrapper div broke the height chain needed by TreeEditorPage's
h-full layout, causing React Flow canvas to collapse to zero height.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: main-content flex layout for tree editor + scrollable pages

Main content area is now flex-col so the ViewTransitionOutlet wrapper
gets an explicit computed height via flex-1 min-h-0. This makes h-full
resolve correctly in the tree editor (React Flow canvas) while still
allowing overflow-y-auto scrolling for normal pages.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: resolve ESLint errors in Button and Skeleton components

- Button: suppress react-refresh/only-export-components for buttonVariants re-export
- Skeleton: replace empty interface with type alias, replace Math.random() with static widths array

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: add PageMeta, animation classes, and layout fixes to remaining pages

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/components/common/StaggerList.tsx

@@ -0,0 +1,43 @@
+import { Children, type ReactNode } from 'react'
+import { cn } from '@/lib/utils'
+
+interface StaggerListProps {
+  children: ReactNode
+  className?: string
+  /** Base delay before the first item animates (ms). Default: 0 */
+  baseDelay?: number
+  /** Delay increment between each item (ms). Default: 50 */
+  staggerMs?: number
+}
+
+/**
+ * Wraps each child in a stagger-item animation container.
+ * Children fade in sequentially with a configurable delay.
+ *
+ * Usage:
+ *   <StaggerList className="grid grid-cols-3 gap-4">
+ *     {items.map(item => <Card key={item.id} ... />)}
+ *   </StaggerList>
+ */
+export function StaggerList({
+  children,
+  className,
+  baseDelay = 0,
+  staggerMs = 50,
+}: StaggerListProps) {
+  const items = Children.toArray(children)
+
+  return (
+    <div className={cn(className)}>
+      {items.map((child, i) => (
+        <div
+          key={i}
+          className="stagger-item"
+          style={{ '--stagger-index': i, animationDelay: `${baseDelay + i * staggerMs}ms` } as React.CSSProperties}
+        >
+          {child}
+        </div>
+      ))}
+    </div>
+  )
+}