Add light mode support (next-themes), JetBrains Mono font, OpenType features

- layout.tsx: ThemeProvider from next-themes, light mode DEFAULT, JetBrains_Mono font
- globals.css: font-mono pointing to correct variable, font-feature-settings cv01+ss03 on body
- next-themes package installed
- Build passes with zero errors

docs/web-lightmode-spec.md

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+CRITICAL REDESIGN REQUIRED. The current Tessera frontend is dark-mode-only and not user-friendly. Implement these changes:
+
+## 1. LIGHT MODE AS DEFAULT
+Rewrite the theme system. shadcn/ui supports light/dark via CSS variables.
+
+- Remove forced `className="dark"` from HTML element in layout.tsx
+- Add ThemeProvider (install next-themes: bun add next-themes)
+- Light mode is DEFAULT. Dark mode via toggle.
+- Use shadcn/ui's built-in CSS variable system (already in globals.css)
+
+Light mode colors:
+- Background: white for canvas, #f8f9fa for panels/sidebar
+- Text: #1a1a2e primary, #4a4a6a secondary, #6b7280 tertiary
+- Borders: #e5e7eb, Cards: white with shadow
+- Accent: #5e6ad2 (works in both modes)
+
+Dark mode (toggled): keep existing Linear-inspired dark theme
+
+## 2. BETTER FONT
+- Primary: 'Inter' from next/font/google with font-feature-settings: 'cv01' 1, 'ss03' 1 (geometric Linear-like character)
+- Monospace: 'JetBrains Mono' for ticket IDs, code, config
+- Headings: tighter letter-spacing (-0.02em)
+- Body: 15px base, line-height 1.5
+
+## 3. UX IMPROVEMENTS
+
+### Ticket list (page.tsx):
+- Inbox-like rows: padding, hover highlight, subtle left border on hover
+- Add checkbox column for future batch actions
+- Clicking row opens detail in split view: list stays on left, detail on right
+- OR simplified: click opens slide-over Sheet from right showing detail
+- "New Ticket" button: prominent with gradient background
+
+### Ticket detail (tickets/[id]/page.tsx):
+- Better conversation hierarchy: customer messages tinted, agent clearly differentiated
+- Properties sidebar: group into Status/Assignment/Details sections with dividers
+- Status dropdown: more prominent (most important action)
+
+### Global:
+- Smooth transitions (150ms ease) on hover states
+- Border radius consistency (8px cards, 6px inputs)
+- Sidebar collapse/expand with hamburger
+- Breadcrumb navigation at top of detail pages
+- Tooltips on icon buttons
+- Split-view or sheet overlay for ticket detail from list
+
+### Command palette:
+- Ensure Cmd+K / Ctrl+K triggers it
+- Add fuzzy ticket search
+- Add quick actions
+
+## 4. IMPLEMENTATION
+- Read current files first
+- Modify existing files, don't delete
+- Preserve api.ts and types.ts
+- Use next-themes for theme switching
+- shadcn/ui CSS variables already in globals.css
+
+## 5. VERIFY
+- `cd web && bun run build` — zero TypeScript errors
+- Both light and dark mode work
+- Font has OpenType features applied
+- Ticket list is inbox-like