refactor: migrate to Tailwind CSS v4 and TypeScript

Replaces PostCSS-based styling with Tailwind CSS v4 via Vite plugin
Converts all .js files to .ts with proper type annotations
Adds comprehensive type definitions for Telegram data structures
Extracts reusable UI components and standardizes class utilities

Improves maintainability by eliminating custom CSS in favor of
Tailwind utilities and design tokens
Enhances type safety across Telegram parsing, env access, and API routes
Centralizes agent guidelines in AGENTS.md following repository standards
Upgrades iconography to astro-icon with Remix Icon integration

Expands accessible HTML patterns including ARIA labels, semantic
navigation, and keyboard interaction support
Refactors static proxy logic into shared utility functions
Consolidates modal and image preview markup for consistency

astro.config.mjs

@@ -5,6 +5,8 @@ import node from '@astrojs/node'
 import vercel from '@astrojs/vercel'
 import edgeone from '@edgeone/astro'
 import sentry from '@sentry/astro'
+import tailwindcss from '@tailwindcss/vite'
+import astroIcon from 'astro-icon'
 import { defineConfig } from 'astro/config'
 import { provider } from 'std-env'
 
@@ -33,6 +35,7 @@ export default defineConfig({
   output: 'server',
   adapter: providers[adapterProvider] || providers.node,
   integrations: [
+    astroIcon(),
     ...(process.env.SENTRY_DSN
       ? [
           sentry({
@@ -51,6 +54,7 @@ export default defineConfig({
       : []),
   ],
   vite: {
+    plugins: [tailwindcss()],
     ssr: {
       noExternal: process.env.DOCKER ? !!process.env.DOCKER : undefined,
       external: [