Migrate frontend to shadcn/ui + add Gitea branch panel in endpoint editor

shadcn/ui migration:
- Installed shadcn components: Button, Input, Label, Card, Badge, Checkbox,
  Switch, Tabs, Dialog, Select, Tooltip, Toaster (sonner)
- Migrated all pages: Login, Dashboard, Settings, Endpoints, EndpointEditor,
  Folders, ApiKeys, Logs
- Replaced react-hot-toast with sonner
- Added CSS variables for theming
- Updated tailwind.config.js for shadcn

Gitea branch panel in EndpointEditor:
- GiteaBranchPanel component: branch selector, save to branch, compare
  with main, create PR, merge, commit history
- New backend endpoints: getEndpointFileContent, commitEndpoint,
  getEndpointCommits, getEndpointFromBranch, commitEndpointToBranch
- Frontend giteaApi: extended with endpoint-specific methods

Fixes:
- Fixed sync-all PostgreSQL-compatible UPDATE LIMIT
- .gitignore: added tmp/

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/tailwind.config.js

@@ -1,5 +1,6 @@
 /** @type {import('tailwindcss').Config} */
 export default {
+  darkMode: ["class"],
   content: [
     "./index.html",
     "./src/**/*.{js,ts,jsx,tsx}",
@@ -18,6 +19,8 @@ export default {
           700: '#1d4ed8',
           800: '#1e40af',
           900: '#1e3a8a',
+          DEFAULT: "hsl(var(--primary))",
+          foreground: "hsl(var(--primary-foreground))",
         },
         dark: {
           50: '#f8fafc',
@@ -31,8 +34,56 @@ export default {
           800: '#1e293b',
           900: '#0f172a',
         },
+        background: "hsl(var(--background))",
+        foreground: "hsl(var(--foreground))",
+        card: {
+          DEFAULT: "hsl(var(--card))",
+          foreground: "hsl(var(--card-foreground))",
+        },
+        popover: {
+          DEFAULT: "hsl(var(--popover))",
+          foreground: "hsl(var(--popover-foreground))",
+        },
+        secondary: {
+          DEFAULT: "hsl(var(--secondary))",
+          foreground: "hsl(var(--secondary-foreground))",
+        },
+        muted: {
+          DEFAULT: "hsl(var(--muted))",
+          foreground: "hsl(var(--muted-foreground))",
+        },
+        accent: {
+          DEFAULT: "hsl(var(--accent))",
+          foreground: "hsl(var(--accent-foreground))",
+        },
+        destructive: {
+          DEFAULT: "hsl(var(--destructive))",
+          foreground: "hsl(var(--destructive-foreground))",
+        },
+        border: "hsl(var(--border))",
+        input: "hsl(var(--input))",
+        ring: "hsl(var(--ring))",
+      },
+      borderRadius: {
+        lg: "var(--radius)",
+        md: "calc(var(--radius) - 2px)",
+        sm: "calc(var(--radius) - 4px)",
+      },
+      keyframes: {
+        "accordion-down": {
+          from: { height: "0" },
+          to: { height: "var(--radix-accordion-content-height)" },
+        },
+        "accordion-up": {
+          from: { height: "var(--radix-accordion-content-height)" },
+          to: { height: "0" },
+        },
+      },
+      animation: {
+        "accordion-down": "accordion-down 0.2s ease-out",
+        "accordion-up": "accordion-up 0.2s ease-out",
       },
     },
   },
-  plugins: [],
+  plugins: [require("tailwindcss-animate")],
 }