feat: show git commit SHA as version in footer

TERM v1.0 → TERM v5ca5e01 (or whatever SHA is building).
GIT_SHA is injected via vite define from Makefile.

web/vite.config.ts

@@ -1,9 +1,14 @@
 import { defineConfig } from 'vite'
 import react from '@vitejs/plugin-react'
 
+const gitSha = process.env.GIT_SHA || 'dev'
+
 // https://vite.dev/config/
 export default defineConfig({
   plugins: [react()],
+  define: {
+    __APP_VERSION__: JSON.stringify(`v${gitSha}`),
+  },
   server: {
     host: '0.0.0.0',
     proxy: {